Draft 

ADVISORY BOARD ON 

RADIATION AND WORKER HEALTH 

National Institute for Occupational Safety and Health

REVIEW OF ORAUT-RPRT-0055: A COMPARISON OF EXOTIC 

TRIVALENT RADIONUCLIDE COWORKER MODELS AT THE 

SAVANNAH RIVER SITE

Contract No. 211-2014-58081 

SCA-TR-RPRT2014-0055 

Prepared by 

R. Barton 

J. Lipsztein 

H. Chmelynski 

J. Stiver 

S. Cohen & Associates 

1608 Spring Hill Road, Suite 400 

Vienna, VA 22182 

November 2014 

Disclaimer 

This document is made available in accordance with the unanimous desire of the Advisory Board on 

Radiation and Worker Health (ABRWH) to maintain all possible openness in its deliberations. However, 

the ABRWH and its contractor, SC&A, caution the reader that at the time of its release, this report is predecisional and has not been reviewed by the Board for factual accuracy or applicability within the 

requirements of 42 CFR 82. This implies that once reviewed by the ABRWH, the Board’s position may 

differ from the report’s conclusions. Thus, the reader should be cautioned that this report is for 

information only and that premature interpretations regarding its conclusions are unwarranted.
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S. COHEN & ASSOCIATES:

Technical Support for the Advisory Board on

Radiation & Worker Health Review of

NIOSH Dose Reconstruction Program

Document No. 

SCA-TR-RPRT2014-0055

Effective Date: 

Draft – November 11, 2014

REVIEW OF ORAUT-RPRT-0055: A 

COMPARISON OF EXOTIC TRIVALENT 

RADIONUCLIDE COWORKER MODELS AT 

THE SAVANNAH RIVER SITE

Page 2 of 84

Task Manager:

________________________ Date: ___________

Joseph Fitzgerald

Supersedes:

N/A

Project Manager:

________________________ Date: ___________

John Stiver, MS, CHP

Reviewers:

 J. Fitzgerald

 J. Stiver

Revision 

Number

Effective 

Date Description of Revision

0 (Draft) 11/11/2014 Initial issue
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TABLE OF CONTENTS 

Abbreviations and Acronyms ..........................................................................................................8

1.0 Introduction and Executive Summary ...............................................................................10

2.0 Evaluation of the Comparison of CTW and NCW Distributions ......................................15

3.0 Additional Findings Related to the Use of OPOS and the Maximum Possible Mean 

Methodology ......................................................................................................................24

4.0 Measurement Variation Among Aliquots of the Same Sample .........................................26

5.0 Analysis of CTW Replicates ..............................................................................................29

6.0 Effect of the Variation of Replicates and Uncertainties on Committed Equivalent 

Doses to the Bone Surface and Committed Effective Doses .............................................33

7.0 Comparison of CTW Intakes with AMW Coworker Model .............................................44

7.1 Claim #[3] ..............................................................................................................44

7.1.1 Intake Scenarios Considered ......................................................................45

7.1.2 Additional Comments ................................................................................47

7.1.3 Conclusion .................................................................................................49

7.2 Claim #[1] ..............................................................................................................49

7.2.1 Intake Scenarios Considered ......................................................................50

7.2.2 Additional Comments ................................................................................50

7.2.3 Conclusion .................................................................................................50

7.3 Claim #[2] ..............................................................................................................50

7.3.1 Intake Scenarios Considered ......................................................................51

7.3.2 Conclusion .................................................................................................52

7.4 Claim #[4] ..............................................................................................................52

7.4.1 Intake Scenarios Considered ......................................................................52

7.4.2 Additional Comments ................................................................................53

7.4.3 Conclusion .................................................................................................53

7.5 Claim #[5] ..............................................................................................................53

7.5.1 Intake Scenarios Considered ......................................................................54

7.5.2 Additional Comments ................................................................................54

7.5.3 Conclusion .................................................................................................55

7.6 Claim #[6] ..............................................................................................................55

7.6.1 Intake Scenarios Considered ......................................................................56

7.6.2 Additional Comments ................................................................................56

7.6.3 Conclusion .................................................................................................56

7.7 Claim #[8] ..............................................................................................................57

7.7.1 Intake Scenarios Considered ......................................................................57

7.7.2 Conclusion .................................................................................................58

7.8 Claim #[9] ..............................................................................................................58

7.8.1 Intake Scenarios Considered ......................................................................59

7.8.2 Additional Comments ................................................................................59

7.8.3 Conclusion .................................................................................................59

7.9 Claim #[10] ............................................................................................................60

7.9.1 Intake Scenarios Considered ......................................................................60

7.9.2 Conclusion .................................................................................................61
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7.10 Claim #[12] ............................................................................................................61

7.10.1 Intake Scenarios Considered ......................................................................61

7.10.2 Conclusion .................................................................................................62

7.10.3 Intake Analysis Findings............................................................................63

8.0 Evaluation of the Completeness of the Trivalent Actinide Bioassay Database .................64

8.1 Analysis of Monitored Job Titles ...........................................................................64

8.2 Analysis of Associated Work Areas ......................................................................66

8.3 Review of Claimant Files Contained in the Coworker Database ..........................66

References ......................................................................................................................................72

Attachment A: Comparison of NCW and CTW Distributions and Geometric Means, 1966 

TO 1989 .............................................................................................................................74
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LIST OF TABLES 

Table 1. Number of Bioassay Results, OPOS Results, and Positive OPOS Results ....................... 16

Table 2. Geometric Mean (GM) and Geometric Standard Deviation (GSD), and 95th

Percentile of Lognormal Distributions .......................................................................... 17

Table 3. Peto-Prentice Test p-Values from RPRT-0055 ................................................................. 21

Table 4. Overview of Single Urinalysis Samples with at least One Positive 

Aliquot Measurement .................................................................................................... 27

Table 5. Ratio and Differential between the Largest and Smallest Measured Aliquot among 

the 484 “All Positive” Samples ..................................................................................... 27

Table 6. Differential between the Largest and Smallest Measure Aliquot among the 571 

Samples Exhibiting both Positive and Less than MDA Measurements ........................ 28

Table 7. Analysis of Replicated Measurements on 31 Urine Samples ............................................ 29

Table 8. Examples of the Variation of Disc Results Related to the Same Urine Sample 

(activities in dpm/1.5L) ................................................................................................. 36

Table 9. Acute Intake of Am-241 Corresponding to an Excretion Rate of 0.3 dpm/d at 

Various Times Post-Exposure ....................................................................................... 37

Table 10. Committed Equivalent Doses to the Bone Surface from an Acute Intake of 

Am-241 Corresponding to an Excretion Rate of 0.3 dpm/day ...................................... 38

Table 11. Predicted 30-Year Committed Equivalent Doses to the Bone Surface for Am-241 

Urine Activities Ranging from 0.3 dpm/1.5 L to 1/5 dpm/1.5 L Utilizing 

Different Sampling Times after Intake .......................................................................... 38

Table 12. Committed Equivalent Doses to the Bone Surface Calculated Assuming a 

Continuous Intake of Am-241 during One Year for Sampling Results 

Ranging from 0.3 to 1.5 dpm/1.5 L ............................................................................... 40

Table 13. Examples of Observed Variations in Disc Results of the Same Sample that are 

Significantly Higher than the MDA (0.3 dpm/1.5 L) .................................................... 40

Table 14. 30-Year Committed Equivalent Doses to the Bone Surface for Different Urine 

Activities and Different Sampling Collection Times .................................................... 41

Table 15. Committed Effective Doses to the Bone Surface Calculated Assuming a 

Continuous Intake during One Year for Varying Sample Activities ............................. 42

Table 16. Trivalent Urinalysis Results during SEC Period for Claim #[3] ..................................... 44

Table 17. Summary of Modeled Intakes .......................................................................................... 46

Table 18. Trivalent Urinalysis Results during SEC Period for Claim #[1] ..................................... 49

Table 19. Summary of Modeled Intakes .......................................................................................... 50

Table 20. Trivalent Urinalysis Results during SEC Period for Claim #[2] ..................................... 51

Table 21. Summary of Calculated Intakes and Intake Comparison ................................................. 51

Table 22. Trivalent Urinalysis Results during SEC Period for Claim #[4] ..................................... 52
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Table 23. Summary of Calculated Intakes and Intake Comparison ................................................. 53

Table 24. Trivalent Urinalysis Results during SEC Period for Claim #[5] ..................................... 54

Table 25. Summary of Calculated Intakes and Intake Comparison ................................................. 54

Table 26. Trivalent Urinalysis Results during SEC Period for Claim #[6] ..................................... 55

Table 27. Summary of Calculated Intakes and Intake Comparison ................................................. 56

Table 28. Trivalent Urinalysis Results during SEC Period for Claim #[8] ..................................... 57

Table 29. Summary of Calculated Intakes and Intake Comparison ................................................. 58

Table 30. Trivalent Urinalysis Results during SEC Period for Claim #[9] ..................................... 58

Table 31. Summary of Calculated Intakes and Intake Comparison ................................................. 59

Table 32. Trivalent Urinalysis Results during SEC Period for Claim #[10] ................................... 60

Table 33. Summary of Calculated Intakes and Intake Comparison ................................................. 60

Table 34. Trivalent Urinalysis Results during SEC Period for Claim #[12] ................................... 61

Table 35. In-Vivo Monitoring Results for Claim #[12] ................................................................... 62

Table 36. Fecal Sampling Results for Claim #[12].......................................................................... 62

Table 37. Overview of Job Titles by Sample Present in Am/Cm/Cf Database during the SEC 

Period ............................................................................................................................. 65

Table 38. Overview of Job Titles by Worker in the Am/Cm/Cf Database 

during the SEC Period ................................................................................................... 65

Table 39. Overview of Work Areas by Samples Present in Am/Cm/Cf Database 

during the SEC Period ................................................................................................... 66

Table 40. Summary of Observed Discrepancies between Claimant Monitoring Records 

and Trivalent Coworker Database ................................................................................. 67

Table 41. Discrepancies Identified between Coworker Database Occupation Assignment and 

Claimant NOCTS/CATI Job Descriptions .................................................................... 69
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LIST OF FIGURES 

Figure 1. Scatter Plot of Geometric Mean (dpm/day) vs. Geometric Standard Deviation .............. 18

Figure 2. Comparison of NCW and CTW Geometric Means, 1966 to 1989 ................................... 19

Figure 3. Comparison of NCW and CTW 95th Percentiles, 1966 to 1989 ...................................... 19

Figure 4. Comparison of Peto-Prentice p-Levels for Testing CTW vs. NCW and for Testing 

CTW vs. NCW+Unk ..................................................................................................... 21

Figure 5. Normalized Test Scores over Time for 1-Sided Peto-Prentice Test ................................. 22

Figure 6. Frequency Distribution of Normalized Test Scores for 1-Sided Peto-Prentice Test ........ 22

Figure 7. Example of a Trivalent Bioassay Logbook Entry ............................................................ 26

Figure 8. Box Plots Showing Spread of Replicated Measurements on 31 Bioassay Samples ........ 30

Figure 9. Coefficient of Variation (%) of Replicated Measurements on 31 Bioassay Samples ...... 31

Figure 10. Coefficient of Variation (%) versus Mean of Replicate Measurements ......................... 31

Figure 11. Coefficient of Variation (%) versus Date of Replicate Measurements .......................... 32

Figure 12. Incident Report for Cm-244 Intake Occurring on 3/27/[redact] .................................... 47

Figure 13. Bioassay Record Located in Claimant’s NOCTS File ................................................... 48

Figure 14. Logbook Record Showing Results for 3/27 and 3/28. Record indicates 

“Do Not Report” ............................................................................................................ 48

Figure 15. Additional Logbook Entries for Claimant Samples on 3/27 and 3/28 ........................... 49
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ABBREVIATIONS AND ACRONYMS 

Advisory Board 

or ABRWH Advisory Board on Radiation and Worker Health 

ALARA as low as reasonably achievable 

Am americium 

AMW all monitored workers 

ANSI American National Standards Institute 

Bq Becquerel 

CATI Computer Assisted Telephone Interview 

Cf californium 

Cm curium 

COV coefficient of variation 

CTW construction trades worker 

d day

DL detection limit

dpm/L disintegrations per minute per liter 

dpm disintegrations per minute 

DOE (U.S.) Department of Energy 

DTPA Diethylene Triamine Penta-Acetic

GM geometric mean 

GSD geometric standard deviation 

h hour 

ICRP International Commission on Radiological Protection 

L liter 

mBq megabecquerel

MC monitoring quantity 

MDA minimum detectable activity 

mrem millirem 

mSv milliseivert 

nCi Nanocurie 

NCRP National Council on Radiation Protection and Measurements 

NCW non-construction trades worker 
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NIOSH National Institute for Occupational Safety and Health 

NOCTS NIOSH/OCAS Claims Tracking System 

NRPB National Radiological Protection Board 

OMINEX Optimization of Monitoring for Internal Exposures 

OPOS one person-one sample 

ORAUT Oak Ridge Associated Universities Team 

Pu plutonium 

ROS regression on order statistics 

RPRT report

SC&A S. Cohen and Associates (SC&A, Inc.) 

SEC Special Exposure Cohort 

SRS Savannah River Site 

Unk unknown (job classification) 
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1.0 INTRODUCTION AND EXECUTIVE SUMMARY 

The proposed methods for reconstructing unmonitored exposure to the trivalent actinides 

Am-241, Cm-244, and Cf-252 are described in RPRT-0055: A Comparison of Exotic Trivalent 

Radionuclide Coworker Models at the Savannah River Site (ORAUT 2012a). The proposed 

coworker model utilizes trivalent actinide urinalysis results that have been transcribed from 

hardcopy bioassay logbooks. The data were analyzed in accordance with the one person-one 

sample (OPOS) methodology outlined in RPRT-0053 (ORAUT 2012b). In addition, two distinct 

job classifications [construction trades worker (CTW) versus non-construction trades worker 

(NCW)] were compared to determine whether coworker stratification was warranted. The main 

conclusion of RPRT-0055 is that there is not a practically significant difference in the magnitude 

of available bioassay data for the two strata and so a single “all worker” coworker model was 

appropriate. Chronic intake rates were calculated utilizing all available worker data, which 

resulted in a single chronic intake rate from the start of the Special Exposure Cohort (SEC) 

period through 1994 (ORAUT 2013). 

During the April 29, 2014, meeting of the Advisory Board on Radiation and Worker Health, 

SC&A was tasked with reviewing RPRT-0055 and associated documentation with a focus on the 

feasibility of reconstructing unmonitored exposures to trivalent actinides using the available 

coworker monitoring data. It should be noted that prior to this review, SC&A had performed 

reviews of RPRT-0053 (ORAUT 2012b) and the Savannah River Site (SRS) SEC Evaluation 

Report Addendum 3 (DCAS 2012). The former outlines the methodology for calculating the 

OPOS statistic, as well as comparing strata to determine if there are appreciable differences in 

the exposure potential for different job classifications. The latter report utilized the trivalent 

actinide database in order to reconstruct unmonitored thorium exposures. Many of the findings 

from those two reviews are therefore germane to the review of RPRT-0055 and so are replicated 

in this report. 

The main body of this report is separated into seven main sections (Sections 2-8):

 Section 2: Evaluation of the Comparison of CTW and NCW Distributions 

 Section 3: Additional Findings Related to the Use of OPOS and Maximum Possible 

Mean Methodology 

 Section 4: Measurement Variation Among Aliquots of the Same Sample 

 Section 5: Analysis of CTW Replicates 

 Section 6: Effect of the Variation of Replicates and Uncertainties on Committed 

Equivalent Doses to the Bone Surface and Committed Effective Doses 

 Section 7: Comparison of CTW Intakes with AMW Coworker Model 

 Section 8: Evaluation of the Completeness of the Trivalent Bioassay Database 

During the course of this review, SC&A identified 18 main findings and 7 observations as 

follows: 
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Finding 1 (formerly Finding 5 of SC&A 2013): SC&A has concluded that NIOSH’s method 

for comparing the measurements of two sets of workers requires that the monitoring protocols of 

the two sets of workers were the same. NIOSH has stated that the protocol for CTW bioassays 

was different. As a result, the method used by NIOSH to compare CTW and NCW Am/Cm/Cf 

data does not meet the requirements for a valid comparison of the two bioassay datasets for the 

1972–1989 period. 

Finding 2 (formerly Finding 6 of SC&A 2013): NIOSH’s coworker model for thorium [and 

Am/Cm/Cf] is based on its conclusion that CTW and NCW bioassay samples are drawn from the 

same distribution. A corollary of Finding [1] above is that NIOSH’s coworker model, which 

combines NCW and CTW data, is based on an invalid comparison, and therefore is not suitable 

for estimating CTW thorium [and Am/Cm/Cf] doses for the 1972–1989 period. 

Finding 3 (formerly Finding 7 of SC&A 2013): The SRS emphasis on incident-related 

monitoring of CTWs at SRS does not necessarily reflect differences between CTW work and 

NCW work. As a result, the emphasis on incident-related monitoring may have missed routine 

exposures for at least some CTW job types. 

Finding 4 (formerly Finding 8 of SC&A 2013): The number of CTW data points is less than 

30 in each aggregated period during 1984–1989. This is less than the minimum number required 

for a valid comparison between CTWs and NCWs. Therefore, NIOSH’s conclusion that CTW 

and NCW sample distributions are the same is not valid for this period. As a result, the coworker 

model based on this conclusion has not been shown to be valid for this period. 

Finding 5 (formerly Finding 9 of SC&A 2013): While NIOSH has not provided disaggregated 

data for 1981 and 1982, the number of CTW data points for 1982 is less than 30. Hence, the data 

for 1982 are also insufficient for a CTW-NCW distribution comparison. 

Finding 6 (formerly Finding 11 of SC&A 2013): NIOSH has not demonstrated that the 

number of CTW samples is sufficient to simultaneously maintain low levels of Type 1 and 

Type 2 errors (for instance, less than 5% for Type 1 errors and less than 15% for Type 2 errors), 

even in the years when CTWs have more than 30 samples. SC&A’s analysis indicates that when 

the geometric standard deviation (GSD) is much larger than the ratio of CTW to NCW geometric 

means (GMs), the rate of Type 2 errors will tend to be high. Type 2 errors occur when the null 

hypothesis (distributions are the same) is incorrectly accepted. 

Finding 7 (formerly Finding 10 of SC&A 2013): Aggregating data over more than 1 year 

without reference to underlying processes and other data is not justifiable. NIOSH should 

provide a technical rationale for treating 1981–1982 and 1987–1989 differently than other years. 

Aggregation over more than 1 year to increase the number of data points is not a suitable 

technical rationale. If no sound basis can be provided for aggregating data over more than 1 

year, NIOSH should do annual aggregating for calculating OPOS values. This is important for 

evaluating NIOSH’s conclusion that CTW and NCW data are drawn from the same distribution. 

Furthermore, aggregation over multiple years rather than a single year to estimate an OPOS 

value increases the risk that the result would represent a mix of thorium exposure and Am/Cm/Cf 

exposure, rendering it scientifically questionable. 
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Finding 8 (formerly Finding 13 of SC&A 2013): NIOSH’s interpretation of the below MDA 

[or detection limit (DL)] results for OPOS calculations is an interpretation of data entry 

conventions that contains an element of arbitrariness. It is systematically claimant unfavorable 

when a large fraction of the results are well below the MDA. This finding applies to all cases 

where NIOSH proposes to use OPOS data as presently calculated for coworker models, 

including those whose data are reviewed in this report (Am, Cm, Cf and thorium), as well as 

others such as neptunium and fission products. 

Finding 9 (formerly Finding 14 of SC&A 2013): NIOSH’s approach to using data well below 

the MDA, including negative numbers and zeros to calculate OPOS values, can sometimes yield 

scientifically meaningless results such as negative OPOS values, implying negative intakes. The 

problem of negative OPOS results is especially prevalent in the 1983–1989 period. 

Finding 10 (formerly Finding 15 of SC&A 2013): The present NIOSH method of calculating 

OPOS data would result in systematically very claimant-unfavorable results in the case of the 

Am, Cm, Cf dataset. This would be true of thorium dose estimates as well as Am, Cm, Cf dose 

estimates. This is because the vast majority of bioassay results for the 1972–1989 period are 

well below the MDA.

Finding 11 (formerly Finding 16 of SC&A 2013): SC&A is concerned that some reported 

results in the logbooks that are above the MDA are averages of results that are both well below 

and well above the MDA. This is much better than the NIOSH OPOS procedure when even 

below MDA results are used at face value, but it is still a concern since such practices vitiate the 

connection between the raw data and the workers’ intake experience in the real world. 

Finding 12 (formerly Finding 19 of SC&A 2013): Many reported OPOS values that are above 

the DL are actually the average of negative and positive normalized disc results, or are the 

average of results with large differences among the different discs derived from the same urine 

sample. Such average results no longer retain an unambiguous connection to the intake of the 

worker, do not represent excretion rates of workers, and therefore should not be used to calculate 

intake rates. 

Finding 13 (formerly Finding 20 of SC&A 2013): Many reported OPOS results below the DL

are the average of normalized disc results that have a large variation between them. This 

indicates that the resultant average of disc results is highly uncertain. Such average results do 

not have an unambiguous connection to the intake of workers, do not represent excretion rates, 

and should not be used to calculate intake rates. 

Finding 14: Given the observed variation in the magnitude of multiple measured aliquots of the 

same sample, SC&A questions whether the dataset is sufficiently accurate and adequate for use 

in reconstructing doses to both monitored and unmonitored workers. NIOSH should examine 

and justify the dataset in the context of the large uncertainties associated with the observed 

measurement variability to justify its use in dose reconstruction. 

Finding 15: NIOSH must demonstrate the usability of the bioassay reported results for trivalent 

actinides in terms of retrospective dose calculations for the individual claimants. Each claim 
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must be analyzed case-by-case, taking into consideration the organ or tissue for which the 

committed effective dose is calculated and its probability of causation. 

Finding 16: NIOSH should review the number of bioassay samples that carry large 

discrepancies in disc activity concentrations, as well as the magnitude of variation in activity 

concentration in individual disc results, in order to establish the adequacy of the available 

records to derive the 50th, 84th and 95th percentile coworker’s intakes for the trivalent actinides. 

Finding 17: Uncertainties observed in the urine in-vitro methodology are very high for the 

sampled claimants, making accurate intake assessments particularly difficult. This is evident in 

multiple instances where differences in disc results for the same sample are significant. 

Additionally, the reported urinalysis activity was very low for one claimant who had a confirmed 

high intake based on fecal and in vivo measurements. This may be due to problems in the urine 

bioassay method. 

Finding 18: The 95th percentile daily intake rates for Am-241 and Cm-244 in the period 1973–

1994 predict excretion rates that are below the DL for the first 10 years of continuous exposure. 

Any worker that had a positive excretion rate during the first 10 years of exposure without an 

indication of a specific incident occurring in a small interval of time before the sampling will be 

misrepresented by the 95th percentile coworker model. 

Observation 1: SC&A noted that many results were excluded from the OPOS analysis for 

various reasons including no apparent date to the sample, sample was marked lost in process, or 

chelation was involved. SC&A identified 52 samples that were excluded, mainly based on a 

missing date, which likely could still be used in the coworker model since the date of the report 

can be used to accurately place the sample in a given year. 

Observation 2: Based on the job title analysis, it is apparent that the monitored worker 

population is not homogeneous but biased towards job types that are more likely to be exposed, 

such as lab technicians/technical assistants and operators. 

Observation 3: The monitoring program is heavily focused on Building 773 (the Savannah 

River Laboratory) where research campaigns were conducted using trivalent actinides and the 

highest potential for intake would likely occur. 

Observation 4: When comparing the coworker database and individual claimant records, 

neither source appears to be complete. However, the additional records found in the claimant 

files had less positive results than the additional records found in the coworker database. 

Therefore, one can conclude that the samples missing from the coworker database do not 

adversely affect the formulation of a coworker model. 

Observation 5: Approximately 1.9% of the claimant samples reviewed showed discrepancies in 

the year of the sample. While this would be considered a “critical error” in the transcription of 

the data, it is very comparable to the critical error rate of 1% described by NIOSH in Section 3.1 

of RPRT-0055. 
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Observation 6: SC&A observed 80 claimant samples that were taken during or in the 

subsequent months following chelation treatment. These samples should be removed from the 

coworker dataset. 

Observation 7: SC&A noted that about 9% of the monitored claimants showed discrepancies 

between the job classifications displayed in the coworker database versus available 

NIOSH/OCAS Claims Tracking System (NOCTS) records. It would be beneficial to perform a 

detailed characterization of how job titles have been established in the coworker database. To 

the extent feasible, an adequate quality assurance activity should be undertaken to ensure that 

monitored workers are correctly placed in the CTW and NCW strata.
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2.0 EVALUATION OF THE COMPARISON OF CTW AND NCW

DISTRIBUTIONS 

Attachment A to RPRT-0055 (ORAUT 2012a) includes regression on order statistics (ROS) and 

effective fit plots for all monitored workers (AMWs), CTWs, and workers not classified as 

CTWs (non-construction trades workers or NCWs) covering the years from 1966 to 1989. A 

fourth group was created that includes all NCWs and those workers with unknown job 

classifications (NCW+unks). Although effective fit plots are shown for all years, the analysis 

presented in RPRT-0055 is based largely on the ROS plots. The effective fit method was applied 

for CTWs and NCWs in the 1981–1982 period and for CTWs in 1984 and 1986. 

This section provides a comparison of the probability distributions obtained from the ROS plots 

for the CTW and NCW strata. Each plot provides the parameters of a lognormal distribution 

obtained by applying the ROS procedure to the OPOS bioassay results for each worker in each 

stratum. There are a total of 19 plots for each stratum, covering time periods from 1 to 3 years, 

usually 1 year. 

The total number of bioassay results, the number of OPOS results (N) and the number of positive 

OPOS results (n) for each period and stratum are shown in Table 1. The table also includes the 

CTW percentage of the total number of records in each category. Although there are a relatively 

large number of NCW records in each period, the number of CTW OPOS results is much smaller 

in all years and categories. The percentage of CTW records ranges from 6% to 35% depending 

on the category. Note that there are less than 30 CTW OPOS records in the period from 1984 

through 1989. When using ROS, the fitted distribution is estimated using only the positive 

OPOS results. There are less than 30 positive CTW OPOS records for the ROS fit in over half of 

the periods analyzed (1966–1968, 1977, 1978 and 1980 through 1989). 

The GM and GSD of the lognormal distributions of urinary excretion rates obtained using the 

ROS procedure are shown in Table 2 for each period and stratum. The table also includes the 

95th percentile of the lognormal distributions and the ratio of the CTW estimates to the NCW 

estimates for each parameter. The year with the largest ratio of the CTW GM to the NCW GM is 

1985. This year is the only year reported to have a statistically significant difference in the PetoPrentice comparison between the CTW and NCW strata reported in RPRT-0055 (Table 4-1: 

Strata Comparisons). The same significant outcome occurs when CTWs are compared with the 

NCW+unk stratum. 

Figure 1 shows a log-scale plot of the GSD versus the GM in the 19 time periods shown in 

Table 2. Except for the points at the upper left of the plot, the two strata appear to have similar 

lognormal distributions. These points account for the 4 very high values of the GSD ranging 

from approximately 19 to 67 in Table 2 for NCWs and CTWs in 1981–1982, and for CTWs in 

1984 and 1986. As noted above, these are the four periods where the effective fit method was 

elected in RPRT-0055. The high GSDs in these four periods led to correspondingly high 

estimates for the 95th percentile of the ROS-fitted lognormal distributions. The 95th percentile of 

the 38 lognormal distributions shown in Table 2 are all less than 2.4 dpm/day, with the exception 

of the 1984 period for CTWs which required the effective fit procedure. 
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Table 1. Number of Bioassay Results, OPOS Results, and Positive OPOS Results 

Total Bioassay OPOS Positive OPOS CTW % of Total Positive

Results* Results* Results* Total OPOS OPOS

(N) (n) Results Results Results

Period NCW CTW NCW CTW NCW CTW (N) (n)

1966–1968 1071 240 329 101 15 8 18 23 35

1969 645 230 277 95 63 27 26 26 30

1970 1593 328 451 124 184 52 17 22 22

1971 1545 292 550 107 431 81 16 16 16

1972 1312 208 525 109 451 93 14 17 17

1973 969 243 509 115 231 56 20 18 20

1974 876 162 357 86 190 46 16 19 19

1975 628 173 356 94 161 48 22 21 23

1976 523 148 346 90 151 47 22 21 24

1977 368 87 292 68 86 16 19 19 16

1978 232 66 171 49 93 24 22 22 21

1979 337 79 234 67 131 37 19 22 22

1980 198 44 178 42 77 22 18 19 22

1981–1982 524 80 379 44 90 16 13 10 15

1983 255 41 232 39 59 17 14 14 22

1984 234 63 210 20 94 11 21 9 10

1985 266 42 214 24 93 18 14 10 16

1986 253 101 219 26 57 11 29 11 16

1987–1989 598 65 336 25 173 12 10 7 6

*Source: RPRT-0055, Table 3-1, Figures A-39 to A-57, and Figures A-72 to A-90. 
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Table 2. Geometric Mean (GM) and Geometric Standard Deviation (GSD), and 95th

Percentile of Lognormal Distributions 

Ratio: CTW/NCW

GM* GSD* 95th Percentile 95th

(dpm/d) (dpm/d) GM GSD Percentile

Period NCW CTW NCW CTW NCW CTW

1966–1968 2.7E-01 1.3E-01 2.93 5.63 1.59 2.32 0.5 1.9 1.5

1969 2.6E-01 5.6E-01 3.34 1.78 1.88 1.46 2.2 0.5 0.8

1970 2.1E-01 2.4E-01 2.65 1.64 1.02 0.53 1.2 0.6 0.5

1971 1.7E-01 1.7E-01 2.59 2.10 0.80 0.58 1.0 0.8 0.7

1972 7.1E-02 7.4E-02 3.34 2.78 0.51 0.39 1.0 0.8 0.8

1973 7.8E-03 9.5E-03 7.71 9.08 0.22 0.36 1.2 1.2 1.6

1974 8.7E-03 1.4E-02 11.66 5.97 0.49 0.26 1.6 0.5 0.5

1975 1.0E-02 9.3E-03 7.26 7.96 0.27 0.28 0.9 1.1 1.0

1976 1.2E-02 1.5E-02 6.63 5.25 0.27 0.23 1.3 0.8 0.9

1977 3.9E-03 2.8E-03 11.32 13.60 0.21 0.21 0.7 1.2 1.0

1978 2.8E-02 1.5E-02 10.64 9.12 1.38 0.57 0.5 0.9 0.4

1979 2.4E-02 2.6E-02 10.82 13.64 1.20 1.94 1.1 1.3 1.6

1980 9.4E-03 9.0E-03 7.20 10.88 0.24 0.46 1.0 1.5 1.9

1981–1982 1.3E-03 2.9E-03 18.81 52.91 0.16 2.00 2.3 2.8 12.7

1983 4.7E-03 1.2E-02 9.10 7.43 0.18 0.33 2.6 0.8 1.9

1984 7.3E-03 5.1E-03 9.15 67.47 0.28 5.24 0.7 7.4 18.8

1985 9.8E-03 5.1E-02 10.35 5.74 0.46 0.91 5.2 0.6 2.0

1986 4.2E-03 1.5E-03 9.00 61.68 0.15 1.32 0.4 6.9 8.5

1987–1989 1.8E-02 9.4E-03 6.11 10.87 0.35 0.48 0.5 1.8 1.4

*Source: RPRT-0055, Figures A-39 to A-57 and A-72 to A-90. 
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Figure 1. Scatter Plot of Geometric Mean (dpm/day) vs. Geometric Standard Deviation 

The GMs for each group of workers in each time period are compared in Figure 2. If the CTW 

and NCW GMs were identical in every year, the plot would have perfect symmetry. Both strata 

have relatively high GMs from 1966 through 1972. In the years after 1972, the GMs are much 

smaller for both groups. There are apparent deviations from symmetry in three periods, 1966–

1968, 1969, and 1985. In 1966–1968, the CTW GM is smaller than the NCW GM, with a ratio 

of 0.5. The year 1969 shows a relatively large difference, although the ratio of the CTW to 

NCW GMs in this period is only 2.2, as compared with the significantly high ratio of 5.2 for 

1985.

Attachment A contains plots comparing the fitted lognormal distributions for the CTW and 

NCW strata in each time period. The GM of each distribution is shown as a vertical dotted line 

in these plots. In most periods, the plotted distributions and GMs are very similar and little 

evidence of a practical difference can be found between the two strata. 

Figure 3 shows a comparison of the 95th percentiles of the lognormal distributions in each period. 

Although the GMs shown in Figure 2 for both groups were distinctly lower in the later years, the 

95th percentiles do not show a similar reduction in the later years. 

1

10

100

0.001 0.01 0.1 1

Geometric Standard Deviation

Geometric Mean (dpm/day)

nonCTW

CTW
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Figure 2. Comparison of NCW and CTW Geometric Means, 1966 to 1989 

Figure 3. Comparison of NCW and CTW 95th Percentiles, 1966 to 1989 
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RPRT-0055 applies hypothesis testing to compare the CTW and NCW strata following the 

procedures described in RPRT-0053 (ORAUT 2012b). Table 4.1 in RPRT-0055 reports the 

results of the Peto-Prentice test comparing the CTW and NCW strata in each period. A similar 

set of Peto-Prentice test results are reported for a comparison of the CTW with the NCW+unk 

strata. The p-values for the two sets of tests are shown in Table 3. The p-values for testing of 

the CTW versus NCW are compared with the p-values for testing CTW versus NCW+unk in 

Figure 4. The plot is very symmetric, indicating that there is little difference if the CTW stratum 

is compared with the NCW or with the NCW+unk strata. For this reason, only the CTW versus 

NCW comparison is addressed in the preceding and following discussions. Significant test 

results have low p-values (p<0.05). A significant difference is observed in 1985, while 

borderline significance is attained in the 1981–1982 and 1983 periods. The period 1985, shown 

with dark shading in Table 3, is the only period reported to have a significant difference using 

the Holm multiple test procedure. Two lightly shaded periods, 1981–1982 and 1983, show 

significant differences on a single-test basis, but do not show a significant difference using the 

multiple testing procedure. 

The p-values for the Peto-Prentice test reported in RPRT-0055 are for a two-sided test for 

inequality of the CTW and NCW strata. The two-sided test will report a significant difference if 

the CTWs significantly exceed the NCWs or if the NCWs significantly exceed the CTWs. A 

one-sided test for inequality will report a significant difference only when the CTW stratum 

significantly exceeds the NCW stratum. The normalized test score (z) for a one-sided test of 

inequality in each period is shown in Figure 5. Here, positive values of z denote periods when 

the CTW distribution exceeds the NCW, and negative values of z denote periods when the NCW 

distribution exceeds the CTW. If the absolute value of the normalized score exceeds 1.96 (i.e., 

outside of the region between the vertical dashed lines in the figure), there is a significant 

difference for that single test. The periods 1981–1982, 1983, and 1985 have scores high enough 

for a significant test result if individual years were to be tested. Of these three periods, the Holm 

cutoff for multiple 2-sided testing shows a significant difference only for 1985. The normal 

scores for these three time periods are all positive and greater than 2, indicating that the CTW 

distribution may exceed the NCW distribution. This information is not available when only the 

p-values for a two-sided test are reported in RPRT-0055. 

The frequency distribution of normalized test scores for a one-sided Peto-Prentice test is shown 

in Figure 6. The distribution is approximately normal with a slight tendency toward the right 

with a mean of +0.23, indicating slightly higher values for the CTW stratum when all periods are 

considered. When the absolute value of the normalized score exceeds 1.96 (marked by the 

vertical dashed lines), there is a significant difference based on that single test. The excretion 

rates calculated for the coworker model are used to calculate intakes. The intakes are estimated 

over periods longer than 1 year. NIOSH applies a multiple hypothesis testing procedure 

designed to reach a single decision regarding difference between strata that applies over all years 

with available data, although this length of time may exceed the actual periods used for intake 

assessment. The multiple hypothesis test procedure should be applied to the same set of years 

used for intake modeling, thus allowing for differences between strata in some multiyear intake 

periods while not in others, rather than a single decision applied to all years with data. Treating 

the 1980s as a separate multiyear period may show significant differences between the two strata 

that otherwise would not be seen when the Holm procedure is applied to all years. 
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Table 3. Peto-Prentice Test p-Values from RPRT-0055 

Period CTW:NCW CTW:NCW+unk

1966–1968 0.355 0.375

1969 0.177 0.179

1970 0.982 0.892

1971 0.806 0.813

1972 0.769 0.705

1973 0.331 0.338

1974 0.854 0.868

1975 0.577 0.547

1976 0.256 0.302

1977 0.359 0.450

1978 0.240 0.219

1979 0.930 0.908

1980 0.276 0.265

1981–1982 0.024 0.032

1983 0.013 0.007

1984 0.126 0.093

1985 0.001 0.001

1986 0.127 0.178

1987–1989 0.680 0.680

Source: RPRT-0055, Table 4-1

Figure 4. Comparison of Peto-Prentice p-Levels for Testing CTW vs. NCW and for 

Testing CTW vs. NCW+Unk 
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Figure 5. Normalized Test Scores over Time for 1-Sided Peto-Prentice Test 

Figure 6. Frequency Distribution of Normalized Test Scores for 1-Sided Peto-Prentice Test 
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SC&A concludes that its findings related to sample size and the quality of the data presented in 

our review of thorium issues at SRS (SC&A 2013) also apply to RPRT-0055 with minor 

modifications (shown in italics). These findings were as follows: 

Finding 1 (formerly Finding 5 of SC&A 2013): SC&A has concluded that NIOSH’s method 

for comparing the measurements of two sets of workers requires that the monitoring protocols of 

the two sets of workers were the same. NIOSH has stated that the protocol for CTW bioassays 

was different. As a result, the method used by NIOSH to compare CTW and NCW Am/Cm/Cf 

data does not meet the requirements for a valid comparison of the two bioassay datasets for the 

1972–1989 period. 

Finding 2 (formerly Finding 6 of SC&A 2013): NIOSH’s coworker model for thorium [and 

Am/Cm/Cf] is based on its conclusion that CTW and NCW bioassay samples are drawn from the 

same distribution. A corollary of Finding [1] above is that NIOSH’s coworker model, which 

combines NCW and CTW data, is based on an invalid comparison, and therefore is not suitable 

for estimating CTW thorium [and Am/Cm/Cf] doses for the 1972–1989 period.

Finding 3 (formerly Finding 7 of SC&A 2013): The SRS emphasis on incident-related 

monitoring of CTWs at SRS does not necessarily reflect differences between CTW work and 

NCW work. As a result, the emphasis on incident-related monitoring may have missed routine 

exposures for at least some CTW job types. 

Finding 4 (formerly Finding 8 of SC&A 2013): The number of CTW data points is less than 

30 in each aggregated period during 1984–1989. This is less than the minimum number required 

for a valid comparison between CTWs and NCWs. Therefore, NIOSH’s conclusion that CTW 

and NCW sample distributions are the same is not valid for this period. As a result, the coworker 

model based on this conclusion has not been shown to be valid for this period. 

Finding 5 (formerly Finding 9 of SC&A 2013): While NIOSH has not provided disaggregated 

data for 1981 and 1982, the number of CTW data points for 1982 is less than 30. Hence, the data 

for 1982 are also insufficient for a CTW-NCW distribution comparison. 

Finding 6 (formerly Finding 11 of SC&A 2013): NIOSH has not demonstrated that the 

number of CTW samples is sufficient to simultaneously maintain low levels of Type 1 and 

Type 2 errors (for instance, less than 5% for Type 1 errors and less than 15% for Type 2 errors), 

even in the years when CTWs have more than 30 samples. SC&A’s analysis indicates that when 

the geometric standard deviation (GSD) is much larger than the ratio of CTW to NCW geometric 

means (GMs), the rate of Type 2 errors will tend to be high. Type 2 errors occur when the null 

hypothesis (distributions are the same) is incorrectly accepted.
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3.0 ADDITIONAL FINDINGS RELATED TO THE USE OF OPOS AND 

THE MAXIMUM POSSIBLE MEAN METHODOLOGY 

RPRT-0055 proposes to average raw worker data to yield an OPOS result for each worker in 

each time period. The comparisons of the distributions of the two groups of workers are made 

using OPOS results derived from the raw data. The period of averaging of raw data is usually, 

but not always, 1 year. As many as 3 years are used in some periods. Additional findings were 

presented in SC&A 2013 that address the use of OPOS in coworker modeling. The findings 

presented in the thorium review also apply to the use of OPOS for the exotic radionuclides. The 

OPOS-related findings were as follows: 

Finding 7 (formerly Finding 10 of SC&A 2013): Aggregating data over more than 1 year 

without reference to underlying processes and other data is not justifiable. NIOSH should 

provide a technical rationale for treating 1981–1982 and 1987–1989 differently than other years. 

Aggregation over more than 1 year to increase the number of data points is not a suitable 

technical rationale. If no sound basis can be provided for aggregating data over more than 1 

year, NIOSH should do annual aggregating for calculating OPOS values. This is important for 

evaluating NIOSH’s conclusion that CTW and NCW data are drawn from the same distribution. 

Furthermore, aggregation over multiple years rather than a single year to estimate an OPOS 

value increases the risk that the result would represent a mix of thorium exposure and Am/Cm/Cf 

exposure, rendering it scientifically questionable. 

Finding 8 (formerly Finding 13 of SC&A 2013): NIOSH’s interpretation of the below MDA 

[or detection limit (DL)] results for OPOS calculations is an interpretation of data entry 

conventions that contains an element of arbitrariness. It is systematically claimant unfavorable 

when a large fraction of the results are well below the MDA. This finding applies to all cases 

where NIOSH proposes to use OPOS data as presently calculated for coworker models, 

including those whose data are reviewed in this report (Am, Cm, Cf and thorium), as well as 

others such as neptunium and fission products. 

Finding 9 (formerly Finding 14 of SC&A 2013): NIOSH’s approach to using data well below 

the MDA, including negative numbers and zeros to calculate OPOS values, can sometimes yield 

scientifically meaningless results such as negative OPOS values, implying negative intakes. The 

problem of negative OPOS results is especially prevalent in the 1983–1989 period. 

Finding 10 (formerly Finding 15 of SC&A 2013): The present NIOSH method of calculating 

OPOS data would result in systematically very claimant-unfavorable results in the case of the 

Am, Cm, Cf dataset. This would be true of thorium dose estimates as well as Am, Cm, Cf dose 

estimates. This is because the vast majority of bioassay results for the 1972–1989 period are well 

below the MDA. 

Finding 11 (formerly Finding 16 of SC&A 2013): SC&A is concerned that some reported 

results in the logbooks that are above the MDA are averages of results that are both well below 

and well above the MDA. This is much better than the NIOSH OPOS procedure when even 

below MDA results are used at face value, but it is still a concern since such practices vitiate the 

connection between the raw data and the workers’ intake experience in the real world. 
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Finding 12 (formerly Finding 19 of SC&A 2013): Many reported OPOS values that are above 

the DL are actually the average of negative and positive normalized disc results, or are the 

average of results with large differences among the different discs derived from the same urine 

sample. Such average results no longer retain an unambiguous connection to the intake of the 

worker, do not represent excretion rates of workers, and therefore should not be used to calculate 

intake rates. 

Finding 13 (formerly Finding 20 of SC&A 2013): Many reported OPOS results below the DL

are the average of normalized disc results that have a large variation between them. This 

indicates that the resultant average of disc results is highly uncertain. Such average results do 

not have an unambiguous connection to the intake of workers, do not represent excretion rates, 

and should not be used to calculate intake rates. 
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4.0 MEASUREMENT VARIATION AMONG ALIQUOTS OF THE 

SAME SAMPLE 

As noted in Findings 12 and 13, the calculated OPOS excretion rates not only represent the 

average of multiple samples over a given timeframe (1–3 years), but also the average of 

measurements within the same sample. An example of an Am/Cm/Cf bioassay logbook is 

shown below in Figure 7. Each line in the figure represents a single voiding which has been split 

into anywhere from 2 to 10 separate aliquots (single measurements were also observed for an 

individual sample). In this case, the sample was split into three aliquots. Only the right half of 

the bioassay logbook is shown in Figure 7, the left half would display other sample information 

such as worker name, volume of sample, payroll number, work area, bottling date, lab received 

date, and sample type (routine, special, follow-up, etc.).

Figure 7. Example of a Trivalent Bioassay Logbook Entry

As seen in the figure, the raw count results for this sample are shown in column 1 (0.039, 0.04, 

and 0.055 dpm/disc), and the raw values are normalized to a daily excretion rate in column 2 

(0.193, 0.198, and 0.348 dpm/1.5L). In this case, 2 of the 3 aliquots measured below the DL of 

0.3 dpm/1.5L, and one measurement was positive (0.348 dpm/1.5L). For the purpose of 

calculating an OPOS value, the three normalized aliquot values are averaged, which results in a 

value of 0.246 dpm/1.5L. This comports with the note in the “Remarks” column of the bioassay 

log; however, it should be noted that the “Report” columns truncate this value at the DL (i.e., 

“<0.3”). 

SC&A expressed significant concerns on the variability in individual samples in its white paper, 

SC&A Review of Addendum 3 to the NIOSH Savannah River Site Special Exposure Cohort (Sec00103) Evaluation Report (SC&A 2013, Section 4.2), and again during recent Work Group 

discussions (ABRWH 2014a, ABRWH 2014b). This is especially true when aliquot 
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measurements of the same urinalysis sample show values both above and below the MDA. To 

gain insight into the prevalence of the observed variability including positive measurements, 

SC&A specifically examined all urinalysis samples displaying at least one aliquot with a positive 

measurement. An overview of these observations is presented in Table 4. As seen in the table, 

only about 12% (1,055 in total) of all urinalysis samples contained at least one positive aliquot 

measurement. Of those 1,055 samples exhibiting a positive measurement, over 54% also 

displayed a negative aliquot measurement that was less than the MDA. 

Table 4. Overview of Single Urinalysis Samples with at least One Positive 

Aliquot Measurement 

Category Total 

Number

Percent of 

All Samples

Percent of All Samples 

with Positive 

Measurements

Total # Individual Urinalysis Samples 8,483 – –

# Urinalysis Samples with at Least One Positive Aliquot 

Measurements 1,055 12.4% –

# Samples with Only Positive Aliquot Measurements 484 5.7% 45.9%

# of Samples with Mixed Positive and Less than MDA Aliquot 

Measurements 571 6.7% 54.1%

SC&A compared the relative difference between the maximum and minimum aliquot 

measurement for the 484 samples in which all measurements were positive by calculating the 

ratio (max/min) and differential (max-min) between the high and low results. This analysis is 

shown in Table 5. The table shows that the ratio for this group averaged just over a factor of 2 

and could range as high as a factor of 230. The rank-ordered 95th percentile ratio was 2.76. The 

differential between the maximum and minimum aliquot in a given sample averaged over 

5 dpm/1.5L (over a factor of 17 times the MDA). The GM of the observed differential was 

0.54 dpm/1.5L, or nearly a factor of 2 times the MDA. 

A similar analysis calculating the differential in the high and low aliquot was performed for the 

571 urinalysis samples that had a mix of positive aliquots and below MDA aliquots. The 

calculated differential is shown in Table 6. The maximum and GM differentials were very 

similar to the “all positive” group, although the average and 95th percentile were much lower. 

Only the differential was considered for this group, because the ratios are severely complicated 

in instances of results showing very low, zero and negative results. 

Table 5. Ratio and Differential between the Largest and Smallest Measured Aliquot 

among the 484 “All Positive” Samples

Category

Ratio

[Max Aliquot/Min Aliquot

(Unitless)

Differential

[Max Aliquot – Min Aliquot]

(dpm/1.5L)

Maximum 231.36 478.6

Average 2.17 5.27

Geometric Mean 1.46 0.54

95th Percentile 2.76 17.15

 
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Table 6. Differential between the Largest and Smallest Measure Aliquot among the 571 Samples 

Exhibiting both Positive and Less than MDA Measurements 

Category

Differential

[Max Aliquot – Min Aliquot]

(dpm/1.5L)

Maximum 431.0

Average 1.75

Geometric Mean 0.49

95th Percentile 2.44

For specific worker examples showing significant variation among the same aliquot 

measurement, please refer to Section 4.2 of SC&A 2013. 

Finding 14: Given the observed variation in the magnitude of multiple measured aliquots of the 

same sample, SC&A questions whether the dataset is sufficiently accurate and adequate for use 

in reconstructing doses to both monitored and unmonitored workers. NIOSH should examine 

and justify the dataset in the context of the large uncertainties associated with the observed 

measurement variability to justify its use in dose reconstruction.

Note: This general issue was discussed in the context of the thorium coworker models during the 

February 26, 2014, Work Group meeting. NIOSH agreed that further research, analysis and 

justification was [sic] warranted on the issue of the variability of multiple measurements of the 

same urinalysis sample. (ABRWH 2014b, pp. 193–198) 
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5.0 ANALYSIS OF CTW REPLICATES 

In Section 7, SC&A examines a set of 13 CTW workers with positive bioassay samples to 

determine if these workers are bounded by the 95th percentile of the coworker model. A total of 

31 bioassay samples were collected from these workers, and multiple aliquots of each sample 

were submitted for laboratory measurement. The results of the replicated measurements are 

summarized in Table 7. The number of replicates ranged from 2 to 9 over the 31 urine samples, 

with a total of 115 replicated measurements. The remaining columns show the mean (μ), 

standard deviation (σ), and coefficient of variation (COV=σ/μ) of the replicated measurements 

on each urine sample. These replicates provide an opportunity to examine the extent of 

measurement error during this period. 

Figure 8 shows a series of box plots, one for each of the 31 urine samples. The range of replicate 

values for each sample is shown by the extent of the “whiskers” drawn above and below each 

box. Two outliers are denoted by small circles and identified by its replicate number. Table 7 

shows the percentage COV of the 31 positive CTW bioassay samples. In Figure 9, the COV for 

each sample is expressed as a percentage of the mean of the replicated measurements for that 

sample. The COV values range from less than 7% for sample 24 (with a set of four replicates) to 

almost 70% for sample 19 (which has an identified outlier in Figure 8). 

In many situations, the COV of replicate measurement as a percentage of the replicate mean will 

depend on the magnitude of the results, with smaller percentage variations at higher magnitudes. 

The scatter plot of the COV versus the logged mean for each sample shown in Figure 10 shows a 

weak association in this direction (R

2

=0.12, t=-1.97). It is also likely the measurement 

techniques will improve over time with a corresponding reduction in the COV of replicate 

measurements. The scatter plot of COV versus time in Figure 11 shows scant evidence for 

improvement over the 10-year time span covered by this set of measurements (R

2

=0.02, t=-0.77). 

Table 7. Analysis of Replicated Measurements on 31 Urine Samples

Sample 

ID

Worker 

ID

Sample 

Number 

Number of 

Replicates

Mean 

μ 

(dpm/1.4L)

Standard 

Deviation σ 

(dpm/1.4L)

Coefficient of 

Variation 

COV=100σ/μ 

(%)

1 1 1 4 0.646 0.209 32.3

2 2 1 2 0.340 0.031 9.1

3 3 1 3 0.862 0.543 63.`0

4 3 2 3 1.211 0.277 22.8

5 3 3 4 2.070 0.502 24.3

6 3 4 3 1.471 0.132 9.0

7 3 5 3 2.018 0.267 13.2

8 3 6 3 2.497 0.610 24.4

9 3 7 5 3.814 1.541 40.4

10 3 8 3 3.955 0.393 9.9

11 4 1 4 0.495 0.322 65.0

12 5 1 2 0.323 0.051 15.8

13 6 1 2 0.365 0.075 20.5

14 7 1 3 0.298 0.136 45.5

15 8 1 2 0.581 0.118 20.2
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Table 7. Analysis of Replicated Measurements on 31 Urine Samples

Sample 

ID

Worker 

ID

Sample 

Number 

Number of 

Replicates

Mean 

μ 

(dpm/1.4L)

Standard 

Deviation σ 

(dpm/1.4L)

Coefficient of 

Variation 

COV=100σ/μ 

(%)

16 8 2 2 0.646 0.067 10.3

17 9 1 4 0.564 0.332 58.8

18 10 1 3 0.400 0.075 18.9

19 11 1 9 0.458 0.316 69.1

20 11 2 4 0.601 0.318 52.9

21 11 3 9 0.856 0.168 19.7

22 12 1 2 0.451 0.228 50.6

23 13 1 4 0.892 0.258 28.9

24 13 2 4 0.983 0.065 6.6

25 13 3 4 1.282 0.163 12.7

26 13 4 2 1.367 0.231 16.9

27 13 5 6 0.608 0.239 39.3

28 13 6 4 0.603 0.087 14.4

29 13 7 4 0.793 0.112 14.1

30 13 8 4 1.593 0.207 13.0

31 13 9 4 11.833 0.931 7.9

Figure 8. Box Plots Showing Spread of Replicated Measurements on 31 Bioassay Samples 

(Outliers, shown as small circles, are identified by a Replicate ID Number.) 
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Figure 9. Coefficient of Variation (%) of Replicated Measurements on 31 Bioassay 

Samples

Figure 10. Coefficient of Variation (%) versus Mean of Replicate Measurements 
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Figure 11. Coefficient of Variation (%) versus Date of Replicate Measurements 
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6.0 EFFECT OF THE VARIATION OF REPLICATES AND 

UNCERTAINTIES ON COMMITTED EQUIVALENT DOSES TO THE 

BONE SURFACE AND COMMITTED EFFECTIVE DOSES 

As explained in Sections 4 and 5, there was a significant variation among the various disc results 

from the same aliquot sample for various workers. In RPRT-0055, the disc1results are averaged 

into a single bioassay result for the purposes of calculating an OPOS result and ultimately a 

coworker intake and dose analysis. In the case of monitored claimants, the “reported” result (as 

described in Section 4) is used for the purpose of retrospective dose reconstruction. 

The maximum accepted uncertainty of a given measurement’s precision and accuracy depends 

on the purpose of the result. In the case of the RPRT-0055, monitoring results are used to 

reconstruct SRS trivalent actinides committed equivalent doses to organs and tissues. The 

maximum acceptable range of activity concentrations in replicate aliquots from the same urine 

sample should be related to an acceptable range of committed equivalent doses to organs. This 

has not been formally defined by NIOSH. 

ANSI 1996 suggests that: 

In the routine monitoring of persons for radiation protection purposes, 

procedures must be established to ensure that workers have exposures measured 

and recorded with a reasonable degree of accuracy so that their exposures can be 

controlled and maintained ALARA, and so that they will not inadvertently during 

the course of their employment exceed the recommended and regulatory limits of 

quarterly or annual exposure. 

The same document points out that, “...it is difficult to rationally specify acceptable 

accuracy on the basis of radiation protection needs.” 

ANSI 1996 was revised in 2011 and does not carry the same advice, although the general 

philosophy is still present. ANSI 2011 states the following concerning adequate measurement 

techniques: 

The goals of any quality-oriented measurement program are to establish 

credibility and to maintain the quality of results within established limits of 

acceptance. To achieve the goal of obtaining quality data, only validated 

standard operating procedures shall be used. Validation of procedure is a value 

judgment in which the performance parameters of the method are compared with 

the requirements for the analytical data. A method that is valid in one situation 

may not be valid in another. Requirements for the data are prerequisite and must 

be established at the beginning of the project planning process for procedure 

selection and validation. When data requirements are not considered properly, 

analytical measurement can be unnecessarily expensive, if the method chosen is 

 

1

 As explained previously, single void bioassay samples were split into multiple aliquots, which were then 

placed on “discs” for the purposes of separately counting each aliquot.
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more accurate than required. On the other hand, if the procedure is less accurate 

than required, the measurement data become inadequate. If the accuracy of the 

procedure is unknown, then the measurement data becomes useless, thereby 

requiring re-measurement. 

NCRP 2009 states: 

Measurement uncertainties for actinides in urine via alpha spectrometry, 

including all sources of error, in indirect bioassay measurements for activity at 

levels near MDA are in the range of 30 %. ... uncertainties in classical (e.g.,

least-squares) analysis, however large, may still be unimportant for operational 

doses falling below one tenth of those limits. Ultimately, since Bayesian tools and 

expertise may not be widely available, each facility needs to determine and justify 

the level of complication and accompanying expense used in the routine 

calculation of doses. 

NCRP 2009 cites the OMINEX Project (Optimization of Monitoring for Internal Exposures), 

which conducted a survey of bioassay laboratories and specifically: 

... compiled the results for 18 laboratories that responded (Hurtgen and 

Cossonnet, 2003). One goal was to determine the optimum analytical conditions, 

and the focus was on alpha-spectrometric measurements of the actinides, 

considered to be among the most challenging analyses routinely conducted. The 

optimum conditions were based on an uncertainty of <25 % for total activity of 

1 mBq in a 24 h sample (urine) with an MDA of 0.1 mBq. The average reported 

by the participating laboratories was an uncertainty of 30 % for 1 mBq in a 24 h 

urine sample (Hurtgen and Cossonnet, 2003). 

The final report on the OMINEX project was published in 2004 as an NRPB W-60 document 

(Etherington et al. 2004). It states that: 

The performance of a particular specification for monitoring (monitoring 

method(s), monitoring interval/times, etc.) can be judged against a defined 

minimum requirement on uncertainty in assessed dose. 

The EURADOS Report 2013-01 (Castellani et al. 2013) states that: 

The effort applied to the evaluation of incorporation monitoring data should 

broadly correspond to the expected level of exposure, and the complexity of the 

case. On the one hand, if the exposure is likely to be very low with respect to the 

dose limits, simple evaluation procedures with a relatively high uncertainty may 

be applied. On the other hand, if the monitoring values indicate the exposure to 

be close to or even above the dose limits, much more sophisticated evaluation 

procedures will need to be applied. In routine monitoring, an explicit assessment 

of the dose is required only if the observed bioassay measurement exceeds a predefined critical monitoring quantity. This critical monitoring quantity MC can be 
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considered as the amount of activity retained or excreted at the end of a 

monitoring period that determines an intake that, if it was repeated for all 

monitoring periods during the accounting year, would result in a value of 

committed effective dose of 0.1 mSv in a year. In the absence of knowledge of the 

exact time of intake, the adopted assumption is to consider that intake took place 

at the central value of the monitoring period (T/2), according to the indication of 

the ICRP publication 78 (ICRP 1997). A recent confirmation of this methodology 

is also reported in the ISO 20553 standard (ISO 2006). The MC for Am-241 is 

3E-5 Bq/d for a maximum monitoring interval of 180 d. So in case of the 

actinides, any significant monitoring value is likely to result in an annual dose of 

more than 0.1 mSv and thus has to be evaluated. 

All the aforementioned documents suggest that the acceptable accuracy of monitoring results 

should depend on the pre-selected purpose of the use of those results. In general, urine bioassay 

monitoring results are used with the objective of radiation protection of workers, and the annual 

assessed doses from those measurements are compared with safe limits. For this reason, the 

accuracy of the bioassay method is established based on the capacity to detect intakes that result 

in committed effective doses of the order of 0.1 mSv (10 mrem). 

NCRP 2009 suggested an uncertainty of <0.25% for a total activity of 1 mBq in a 24-h sample 

(urine), with an MDA of 0.1 mBq under optimum conditions. In the case of this review, the 

method used to measure the trivalent actinides in urine has a DL of 0.3 dpm/1.5L, about 

5E-3 Bq/day, which is higher than both values suggested by NCRP 2009 to calculate the 

uncertainties. Thus, the uncertainty suggested by the NCRP 2009 does not apply, for two 

reasons: 

- The method does not apply to the optimum conditions 

- The objective on the use of the bioassay results is not the assessment of effective doses 

for radiation protection purposes 

The “reported” bioassay results are used by NIOSH to calculate the intakes and committed 

equivalent doses to tissues and organs of individual claimant workers. In addition, they are also 

used to calculate coworkers’ intakes and committed equivalent doses to be applied to 

unmonitored workers. 

Assuming that the activity concentration in urine was due to intakes of Am-241, SC&A has 

evaluated the consequences of the variations on disc results in the committed equivalent doses to 

bone surface, which is the tissue with the highest committed dose per unit intake. This selection 

did not take into account the probability of cancer induction in bone surface as compared to other 

organs and tissues and thus the committed equivalent dose to bone surface was only used as an 

example. For this analysis, SC&A has focused on a 20–50 year committed equivalent dose using 

examples of variation in disc results with reported values near the DLs, as well as reported 

values much higher than the MDA. SC&A uses the term “variation” to mean the comparison of 

different disc results from the same urine sample. As there are many results calculated from only 

two discs, variation among discs was used instead of any other potential statistical measure of 

dispersion. The aim of the comparison is focused on the difference in committed equivalent 
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doses to the bone surface, calculated independently for each disc result from the same urine 

sample. 

The analysis comparisons contained herein are only listed as examples. The validity of each 

bioassay result should be analyzed individually by NIOSH while taking into account the 

objective of the specific dose reconstruction or assignment of coworker intakes for the 

unmonitored worker. The following table (Table 8) contains selected examples on variations of 

disc results for reported results in the range of 0.3 to 1 dpm/1.5 L. 

Table 8. Examples of the Variation of Disc Results Related to the Same Urine Sample 

(activities in dpm/1.5L) 

Worker

Identifier Type

dpm/

1.5L

(1)

dpm/

1.5L

(2)

dpm/

1.5L

(3)

dpm/

1.5L

(4)

dpm/

1.5L

(5)

dpm/

1.5L

(6)

dpm/

1.5L

(7)

dpm/

1.5L

(8)

Report/

Average

A Routine 0.588 1.036 0.535 0.123 0.6

L Follow-up 0.479 0.594 0.511 1 0.6

K Routine 0.621 0.079 0.35

W Special 0.526 0.714 0.142 0.378 0.4

LO Follow-up 1.03 -0.309 0.999 0.575 0.6

D Special 0.24 0.92 0.6

D Follow-up 0.357 0.04 0.656 0.099 1.609 1.423 1.144 0.8 0.8

E Routine 0.435 0.534 0.615 1.03 0.7

H Follow-up 0.333 0.679 1.094 0.806 0.7

J 4 0.627 0.341 0.96 0.6

D 2 0.312 1.19 0.352 0.6

B Follow-up 0.558 1.253 0.926 0.9

IW Special 0.304 1.598 0.684 0.9

J Follow-up 0.922 0.523 1.047 0.656 0.8

WP Follow-up 0.567 1.025 1.587 0.332 0.9

JE Follow-up 0.44 0.697 1.27 1.245 0.9

I Routine 1.455 0.376 0.9

B Follow-up 0.312 0.602 1.31 0.528 0.6

R Follow-up 1.015 0.412 0.948 0.614 0.416 0.741 0.7

RL Routine 1.083 0.654 0.533 0.7

The following table (Table 9) of acute intakes was derived assuming an Am-241 concentration in 

urine equal to 0.3 dpm/1.5 L for samples taken at various times after intake. For example, if the 

concentration of Am -241 in urine was 0.3 dpm/1.5L at 2 days after the intake, the corresponding 

intake is 1.3 × 103dpm (22 Bq). If the concentration of Am -241 in urine was 0.3 dpm/1.5 L at 

10 days after the intake, the corresponding intake is 6.2 × 103 dpm (100 Bq). If the concentration 

of Am -241 in urine was 0.3 dpm/1.5 L at 60 days after the intake, the corresponding intake is 

1.6 × 104dpm (270 Bq). 
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The excretion of 1.5 liters may be considered as a daily excretion rate. ICRP Publication 23 

(ICRP 1975) suggests an excretion rate of 1.4 liters per day for the standard man, while the most 

recent publication (ICRP 2002) suggests a standard daily excretion rate of 1.6 liters for adult 

males. The predicted activity fractions per unit intake in a 24-hour urine sample, as defined in 

ICRP 78 (ICRP 1997), were used in this analysis. 

Table 9. Acute Intake of Am-241 Corresponding to an Excretion Rate of 0.3 dpm/d at 

Various Times Post-Exposure 

Time After

Acute Intake

(days)

ICRP 78

Predicted

Fraction of 

Intake

in 24-h Urine

Intake

Corresponding

to the MDA (dpm)

Intake

Corresponding

to the MDA 

(Bq)

1 1.8E-03 1.7E+02 2.8E+00

2 2.3E-04 1.3E+03 2.2E+01

3 1.3E-04 2.3E+03 3.8E+01

4 9.0E-05 3.3E+03 5.6E+01

5 7.2E-05 4.2E+03 7.0E+01

6 6.3E-05 4.8E+03 8.0E+01

7 5.8E-05 5.2E+03 8.7E+01

8 5.4E-05 5.6E+03 9.3E+01

9 5.2E-05 5.9E+03 9.8E+01

10 4.9E-05 6.2E+03 1.0E+02

15 3.9E-05 7.7E+03 1.3E+02

30 2.6E-05 1.1E+04 1.9E+02

60 1.9E-05 1.6E+04 2.7E+02

90 1.6E-05 1.9E+04 3.2E+02

180 1.1E-05 2.7E+04 4.5E+02

The bone surface is the tissue receiving the highest committed dose resulting from intakes of 

Am-241. Table 10 shows the 20 to 50 year committed doses to the bone surface corresponding 

to the acute intakes of Am-241 shown in Table 9. The dose coefficients per unit intake were 

taken from the ICRP software Database of Dose Coefficients: Workers and Members of the 

Public (ICRP 2001). 
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Table 10. Committed Equivalent Doses to the Bone Surface from an Acute Intake of 

Am-241 Corresponding to an Excretion Rate of 0.3 dpm/day 

Time⃰

(Days)

Intake

(Bq)

20-y Dose 

(rem)

25-y Dose 

(rem)

30-y Dose 

(rem)

40-y Dose 

(rem)

50-y Dose 

(rem)

1 2.8E+00 1.6E-01 1.9E-01 2.2E-01 2.7E-01 3.1E-01

2 2.2E+01 1.2E+00 1.5E+00 1.7E+00 2.1E+00 2.4E+00

3 3.8E+01 2.1E+00 2.6E+00 3.0E+00 3.7E+00 4.2E+00

4 5.6E+01 3.1E+00 3.8E+00 4.3E+00 5.4E+00 6.2E+00

5 7.0E+01 3.9E+00 4.7E+00 5.4E+00 6.7E+00 7.7E+00

6 8.0E+01 4.5E+00 5.4E+00 6.2E+00 7.6E+00 8.8E+00

7 8.7E+01 4.9E+00 5.9E+00 6.8E+00 8.3E+00 9.6E+00

8 9.3E+01 5.2E+00 6.3E+00 7.2E+00 8.9E+00 1.0E+01

9 9.8E+01 5.5E+00 6.6E+00 7.6E+00 9.4E+00 1.1E+01

10 1.0E+02 5.8E+00 7.0E+00 8.0E+00 9.9E+00 1.1E+01

15 1.3E+02 7.2E+00 8.7E+01 1.0E+01 1.2E+01 1.4E+01

30 1.9E+02 1.1E+01 1.3E+01 1.5E+01 1.8E+01 2.1E+01

60 2.7E+02 1.5E+01 1.8E+01 2.1E+01 2.6E+01 2.9E+01

90 3.2E+02 1.8E+01 2.1E+01 2.5E+01 3.1E+01 3.5E+01

180 4.5E+02 2.5E+01 3.1E+01 3.5E+01 4.4E+01 5.0E+01

 ⃰ Time after intake, when urine sample was analyzed with a concentration of Am-241 in urine equal to 0.3 dpm/d 

The following table (Table 11) shows the 30-year committed equivalent dose to bone surface for 

urine activity results varying from 0.3 dpm/1.5 L to 1.5 dpm/1.5 L. Using Table 11, it is possible 

to visualize the order of magnitude of the uncertainties on committed equivalent doses to the bone 

surface, produced for each bioassay result, if the disc results were used independently to calculate 

the dose. 

Table 11. Predicted 30-Year Committed Equivalent Doses to the Bone Surface for Am-241 

Urine Activities Ranging from 0.3 dpm/1.5 L to 1/5 dpm/1.5 L Utilizing Different Sampling 

Times after Intake

Time between 

Sample and 

Intake (days)

30-y Dose based 

on a Urine 

Activity of 

0.3 dpm/1.5 L 

(rem)

30-y Dose based 

on a Urine 

Activity of 

0.6 dpm/1.5 L 

(rem)

30-y Dose based 

on a Urine 

Activity of 

0.9 dpm/1.5 L 

(rem)

30-y Dose based 

on a Urine 

Activity of 

1.2 dpm/1.5 L 

(rem)

30-y Dose 

based on a 

Urine Activity 

of 1.5 dpm/1.5 

L (rem)

1 2.2E-01 4.4E-01 6.6E-01 8.8E-01 1.1E+00

2 1.7E+00 3.4E+00 5.0E+00 6.7E+00 8.4E+00

3 3.0E+00 6.0E+00 8.9E+00 1.2E+01 1.5E+01

4 4.4E+00 8.7E+00 1.3E+01 1.7E+01 2.2E+01

5 5.4E+00 1.1E+01 1.6E+01 2.2E+01 2.7E+01

6 6.2E+00 1.2E+01 1.9E+01 2.5E+01 3.1E+01

7 6.8E+00 1.4E+01 2.0E+01 2.7E+01 3.4E+01

8 7.2E+00 1.4E+01 2.2E+01 2.9E+01 3.6E+01

9 7.6E+00 1.5E+01 2.3E+01 3.1E+01 3.8E+01

10 8.0E+00 1.6E+01 2.4E+01 3.2E+01 4.0E+01
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Table 11. Predicted 30-Year Committed Equivalent Doses to the Bone Surface for Am-241 

Urine Activities Ranging from 0.3 dpm/1.5 L to 1/5 dpm/1.5 L Utilizing Different Sampling 

Times after Intake

Time between 

Sample and 

Intake (days)

30-y Dose based 

on a Urine 

Activity of 

0.3 dpm/1.5 L 

(rem)

30-y Dose based 

on a Urine 

Activity of 

0.6 dpm/1.5 L 

(rem)

30-y Dose based 

on a Urine 

Activity of 

0.9 dpm/1.5 L 

(rem)

30-y Dose based 

on a Urine 

Activity of 

1.2 dpm/1.5 L 

(rem)

30-y Dose 

based on a 

Urine Activity 

of 1.5 dpm/1.5 

L (rem)

15 1.0E+01 2.0E+01 3.0E+01 4.0E+01 5.0E+01

30 1.5E+01 3.0E+01 4.5E+01 6.0E+01 7.5E+01

60 2.1E+01 4.2E+01 6.2E+01 8.3E+01 1.0E+02

90 2.5E+01 5.0E+01 7.5E+01 9.9E+01 1.2E+02

180 3.6E+01 7.1E+01 1.1E+02 1.4E+02 1.8E+02

For example, for worker J in Table 8, one bioassay sample produced three disc results of 

approximately 0.3, 0.6, and 0.9 dpm/1.5 L. If those results were analyzed independently, and if 

the urine sample was taken 10 days after the intake, a variation from 0.3 to 0.6 dpm/1.5 L 

produces an increase of 8 rem in the 30-year committed dose to the bone surface (increase from 

8 rem to 16 rem). If the sample was taken 30 days after the intake instead of 10 days, the 

uncertainty in the 30-year committed dose to the bone is 15 rem (increase in bone surface dose 

from 15 rem to 30 rem). In addition, a variation in urine result from 0.3 to 0.9 dpm/1.5 L 

produces an increase in bone surface dose of 16 rem (sample taken 10 days after intake) and 

30 rem (sample taken 30 days after the intake). 

Similarly, for worker D in Table 8, one bioassay sample produced 3 disc results of approximately 

0.3, 1.2, and 0.3 dpm/1.5 L. A variation from 0.3 to 1.2 dpm/1.5 L for a sample taken 10 days 

after the intake results in an increase of 24 rem in the committed 30-year dose to the bone (an 

increase from 8 rem to 32 rem). If the sample was taken 30 days after the intake, there is a 45 rem 

increase (an increase from 15 rem to 60 rem). 

As seen in Table 8, there were various disc results from the same sample of urine with variations 

similar to the variations shown in the above examples. In general, derivation of coworker 

intakes and doses assumes a continuous or chronic intake. If one assumes a continuous intake of 

Am-241 during a 1-year period with a sample taken at the end of the year, the committed 

equivalent doses to the bone surface can be derived for urine results varying from 0.3 to 

1.5 dpm/1.5 L, the results of which are shown in Table 12. 
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Table 12. Committed Equivalent Doses to the Bone Surface Calculated Assuming a 

Continuous Intake of Am-241 during One Year for Sampling Results 

Ranging from 0.3 to 1.5 dpm/1.5 L 

Bioassay

Result 

(dpm/1.5L)

20y Dose to the 

Bone Surface 

(rem)

25y Dose to the 

Bone Surface 

(rem)

30y Dose to the 

Bone Surface 

(rem)

40y Dose to the 

Bone Surface 

(rem)

50y Dose to the 

Bone Surface 

(rem)

0.3 1.4E+01 1.7E+01 2.0E+01 2.4E+01 2.8E+01

0.6 2.8E+01 3.4E+01 3.9E+01 4.9E+01 5.6E+01

0.9 4.2E+01 5.1E+01 5.9E+01 7.3E+01 8.4E+01

1.2 5.6E+01 6.8E+01 7.9E+01 9.7E+01 1.1E+02

1.5 7.0E+01 8.5E+01 9.8E+01 1.2E+02 1.4E+02

As seen in Table 12, a variation from 0.3 to 1.5 dpm/1.5 L of Am-241 in a bioassay result 

produces an increase of 59 rem in the 30-year committed equivalent dose to the bone surface (an 

increase from 20 rem to 79 rem). 

As the urine results became significantly higher than the MDA, the uncertainty in the committed 

doses due to differences in disc results become more significant. Table 13 provides several 

examples of observed variations in disc results from the same urine sample where the activity in 

each disc is much higher than the MDA. 

Table 13. Examples of Observed Variations in Disc Results of the Same Sample that are 

Significantly Higher than the MDA (0.3 dpm/1.5 L)

Worker

Identifier Type dpm/1.5L(1)

dpm/1.5L

(2)

dpm/1.5L

(3)

dpm/1.5L

(4)

dpm/1.5L

(5)

dpm/1.5L

(6)

Report/

Average

BL1 Follow-up 3.58 4.14 1.65 1.95 2.8

BL2 Follow-up 1.4 3.93 1.17 2.2

B Follow-up 1.361 1.899 1.547 2.996 2.41 3.076 2.2

J Follow-up 2.425 3.1 2.503 1.314 1.434 2

BR Follow-up 1.28 0.862 2.142 2.872 1.8

W Special 1.863 3.321 2.306 2.5

Table 14 shows the 30-year committed equivalent doses to the bone surface from Am-241 

activity urine results varying from 1.2 dpm/1.5 L and 3.9 dpm/1.5 L. 
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Table 14. 30-Year Committed Equivalent Doses to the Bone Surface for Different Urine 

Activities and Different Sampling Collection Times 

Time Between 

Sample and 

Intake

(days)

30-Year Committed Equivalent Dose to the Bone Surface (rem) Based on Sample 

Activities Ranging from 1.2 to 3.9 dpm/1.5 L

1.2 

dpm/1.5L

1.5 

dpm/1.5L

1.8 

dpm/1.5L

2.1 

dpm/1.5l

2.4 

dpm/1.5L

3.6 

dpm/1.5L

3.9 

dpm/1.5L

1 8.8E-01 1.1E+00 1.3E+00 1.5E+00 1.8E+00 2.6E+00 2.9E+00

2 6.7E+00 8.4E+00 1.0E+01 1.2E+01 1.3E+01 2.0E+01 2.2E+01

3 1.2E+01 1.5E+01 1.8E+01 2.1E+01 2.4E+01 3.6E+01 3.9E+01

4 1.7E+01 2.2E+01 2.6E+01 3.0E+01 3.5E+01 5.2E+01 5.7E+01

5 2.2E+01 2.7E+01 3.3E+01 3.8E+01 4.4E+01 6.5E+01 7.1E+01

6 2.5E+01 3.1E+01 3.7E+01 4.3E+01 5.0E+01 7.4E+01 8.1E+01

7 2.7E+01 3.4E+01 4.1E+01 4.7E+01 5.4E+01 8.1E+01 8.8E+01

8 2.9E+01 3.6E+01 4.3E+01 5.1E+01 5.8E+01 8.7E+01 9.4E+01

9 3.1E+01 3.8E+01 4.6E+01 5.3E+01 6.1E+01 9.2E+01 9.9E+01

10 3.2E+01 4.0E+01 4.8E+01 5.6E+01 6.4E+01 9.6E+01 1.0E+02

15 4.0E+01 5.0E+01 6.0E+01 7.0E+01 8.0E+01 1.2E+02 1.3E+02

30 6.0E+01 7.5E+01 8.9E+01 1.0E+02 1.2E+02 1.8E+02 1.9E+02

60 8.3E+01 1.0E+02 1.2E+02 1.5E+02 1.7E+02 2.5E+02 2.7E+02

90 9.9E+01 1.2E+02 1.5E+02 1.7E+02 2.0E+02 3.0E+02 3.2E+02

180 1.4E+02 1.8E+02 2.1E+02 2.5E+02 2.8E+02 4.3E+02 4.6E+02

For Worker BL2 in Table 13, one bioassay result produced 3 disc results of 1.4, 3.9, and 

1.17 dpm/1.5 L. If those results were analyzed independently and it is assumed the urine sample 

was taken 10 days after the intake, a variation from 1.2 dpm/1.5 L to 3.9 dpm/1.5 L produces an 

increase of 68 rem in the committed 30-year dose to the bone surface (an increase from 32 rem to 

100 rem). If the sample was taken 30 days after the intake, the uncertainty in the 30-year 

committed effective dose to the bone surface is 130 rem (the dose increases from 60 rem to 

190 rem). 

The following table (Table 15) shows the variation in committed effective doses for continuous 

Am-241 intake during 1 year with an end-of-the-year sample activity ranging from 1.2 to 

3.9 dpm/1.5 L. As previously stated, the derivation of coworker intakes and doses assumes a 

continuous/chronic exposure. 
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Table 15. Committed Effective Doses to the Bone Surface Calculated Assuming a 

Continuous Intake during One Year for Varying Sample Activities 

Sample Activity 

(dpm/1.5L)

20y dose

(rem)

25y dose

(rem)

30y dose

(rem)

40y dose

(rem)

50y dose

(rem)

1.2 5.6E+01 6.8E+01 7.9E+01 9.7E+01 1.1E+02

1.5 7.0E+01 8.5E+01 9.8E+01 1.2E+02 1.4E+02

1.8 8.4E+01 1.0E+02 1.2E+02 1.5E+02 1.7E+02

2.1 9.8E+01 1.2E+02 1.4E+02 1.7E+02 2.0E+02

2.4 1.1E+02 1.4E+02 1.6E+02 1.9E+02 2.3E+02

2.7 1.3E+02 1.5E+02 1.8E+02 2.2E+02 2.5E+02

3.0 1.4E+02 1.7E+02 2.0E+02 2.4E+02 2.8E+02

3.3 1.5E+02 1.9E+02 2.2E+02 2.7E+02 3.1E+02

3.6 1.7E+02 2.0E+02 2.4E+02 2.9E+02 3.4E+02

3.9 1.8E+02 2.2E+02 2.6E+02 3.2E+02 3.7E+02

Table 15 shows that when the Am-241 activity concentration in urine varies from 1.2 to 

3.9 dpm/1.5 L, the derived 30-year committed effective doses to bone surface varies from 79 rem 

to 260 rem. 

Tables 11–15 are only examples of the fluctuation in committed effective doses to the bone 

surface when disc results are evaluated independently. The tables show the dependency of the 

bone surface dose on the uncertainties in the bioassay results. NIOSH should analyze the 

differences in disc results of each bioassay result and evaluate their influence on the ability to 

calculate equivalent doses to various tissues and organs, as well as the consequences in terms of 

calculating the probability of causation. 

In a similar way, NIOSH should analyze the bioassay results with significant differences in disc 

values and determine their influence on the ability of deriving coworker intakes for the 

unmonitored worker. It also must be noted that there are many urine sample results with very 

high activity as a consequence of the treatment with DTPA. Some of those samples show very 

large discrepancies among discs from the same urine sample. Those results cannot be used to 

calculate doses using the standard ICRP models. They also should not be used to calculate 

coworker intake and are thus outside the scope of this review. 

In conclusion, SC&A has pointed out that the SRS method to analyze urine samples for the 

trivalent actinides carries significant variation among the various disc results from the same 

sample. The acceptable accuracy of monitoring results depends on the pre-selected purpose on 

the use of those results. Using Am-241 as an example, SC&A has shown that variations in 

activity concentrations in the same bioassay sample produce significant uncertainties in 

committed equivalent doses to the bone surface. 

Finding 15: NIOSH must demonstrate the usability of the bioassay reported results for trivalent 

actinides in terms of retrospective dose calculations for the individual claimants. Each claim 
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must be analyzed case-by-case, taking into consideration the organ or tissue for which the 

committed effective dose is calculated and its probability of causation. 

Finding 16: NIOSH should review the number of bioassay samples that carry large 

discrepancies in disc activity concentrations, as well as the magnitude of variation in activity 

concentration in individual disc results, in order to establish the adequacy of the available 

records to derive the 50th, 84th and 95th percentile coworkers’ intakes for the trivalent actinides. 

 
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7.0 COMPARISON OF CTW INTAKES WITH AMW 

COWORKER MODEL 

SC&A identified several claimants among the monitored subcontractor population who also had 

at least one positive reported bioassay sample. These claims were examined and intake analyses 

were performed for comparison against the 95th percentile coworker assignment. If an incident 

was identified in the claimant record, the date of the incident was used to calculate an acute 

intake. If no specific incident was identified, both a chronic intake scenario and an acute intake 

scenario were evaluated. For the chronic intake scenario, it was assumed that the claimant was 

exposed beginning in 1973 up through the date of the positive bioassay sample. Acute intake 

evaluations assume that the intake occurred midway between the positive bioassay sample and 

the previous sample. This is in accordance with the ICRP recommendations for situations in 

which the exact date of the intake is unknown. The intake evaluations for each identified 

claimant are presented below. Overall findings based on this analysis are presented at the end of 

this section.

7.1 CLAIM #[3]

Employment Period: [Redacted]–[Redacted]

Job Title: [Redacted] & [Redacted]

The claimant was involved in an acute curium incident in March of 1975. The trivalent bioassay 

results for this claimant during the SEC period are shown in Table 16. 

Table 16. Trivalent Urinalysis Results during SEC Period for Claim #[3]

Date

Bioassay Value (dpm/1.5L)

Database Additional Comments

Result(s)a

Logbook 

Report 

Valueb

NOCTS 

Resultc

5/25/[redact] 0 <0.3 <0.3

1/31/[redact] 0 <0.3 <0.3

5/16/[redact] 0 <0.3 <0.3

11/7/[redact] 0 <0.3 <0.3

3/27/[redact]

3.699, 5.64, 

4.02, 1.033, 

4.68

3.6 3.2, 1.7, 

50

Note: NOCTS results do not agree with logbook results.

Values in “Logbook Report Value” column appear in the 

coworker database and correspond to values contained in 

the “Remarks Column” of the hardcopy record.

Incident occurred on this date.

Sample designation: “Special”

3/27/[redact]

1.863, 

3.321, 2.306 2.5 3.2, 1.7, 50

Note: NOCTS results do not agree with logbook results.

Values in “Logbook Report Value” column appear in the 

coworker database and correspond to values contained in 

the “Remarks Column” of the hardcopy record.

Sample designation: “Special”

3/27/[redact]

3.798, 

4.496, 3.572 4

3.2, 1.7, 

50

Note: NOCTS results do not agree with logbook results.

Values in “Logbook Report Value” column appear in the 

coworker database and correspond to values contained in 

the “Remarks Column” of the hardcopy record.

Sample designation: “Special”
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Table 16. Trivalent Urinalysis Results during SEC Period for Claim #[3]

Date

Bioassay Value (dpm/1.5L)

Database Additional Comments

Result(s)a

Logbook 

Report 

Valueb

NOCTS 

Resultc

3/28/[redact]

2.208, 2.82, 

1.75, 1.5 1.4 50 Note: NOCTS results do not agree with logbook resultsSample designation: “Follow-up”

3/28/[redact]

1.52, 1.603, 

1.29 1.5 50 Note: NOCTS results do not agree with logbook resultsSample designation: “Special”

3/28/[redact]

2.339, 

2.029, 1.685 2 50 Note: NOCTS results do not agree with logbook resultsSample designation: “Special”

3/31/[redact]

1.409, 

1.405, 0.82 1.2 1.2 Sample designation: “Special”

4/1/[redact]

0.304, 

1.598, 0.684 0.9 0.9 Sample designation: “Special”

5/5/[redact] 0, 0.57 <0.3 <0.3 Note: Positive measurements mixed with “0” 

measurements. Sample designation: “Follow-up”

5/7/[redact] 0, 0.586 <0.3 <0.3 Sample designation: “Follow-up”

6/2/[redact] 0.194 <0.3 <0.3

9/4/[redact] 0.093 <0.3 <0.3

11/20/[redact] 0 <0.3 <0.3

2/5/[redact] 0 <0.3 <0.3

5/27/[redact] 0.07 <0.3 <0.3

Sample designation: “5” 

Record in NOCTS is listed as “Pu,” but lists the MDA 

for “Am” of <0.3 and not the “Pu” MDA of <0.3.

11/5/[redact] 0 <0.3 <0.3

5/13/[redact] 0 <0.3 <0.3 Sample designation: “5”

2/21/[redact] 0.095 <0.3 <0.3 Sample designation: “12”

1/7/[redact] Missing Missing <0.3

12/14/[redact] Missing Missing <0.3

a These represent the normalized aliquot measurements in dpm/1.5 L found in the electronic coworker database 

transcribed by NIOSH/ORAUT from hardcopy bioassay logbooks. 

b Each logbook entry also contained a “reported” value in addition to the raw results shown in column 2. 

c This column represents the data provided by DOE for the individual claim for the purposes of dose 

reconstruction. 

7.1.1 Intake Scenarios Considered 

Claimant was involved in an intake incident involving Cm-244 in Cell 8 of 773A (see redacted 

incident report in Figure 12). Based on the incident report, the resulting bioassay results were 

reported as: 

3/27/[redact]: 3.2 dpm/1.5L

3/28/[redact]: 1.7 dpm/1.5L

3/31/[redact]: 1.2 dpm/1.5L

4/1/[redact]: 0.9 dpm/1.5L

It must be noted that these results are not compatible with the expected decrease in excretion 

rates for Type M Cm-244, applying ICRP 71 biokinetic model (ICRP 1995). One would expect 

the urinalysis sample to be approximately 20 times lower on March 31st than it was on March 
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28th. Nonetheless, the most claimant-favorable intake rates were calculated using variable 

combinations of the four results listed in the incident report (note Additional Comments). For 

the purposes of this analysis, 1.5 liters was considered to be the daily excretion rate.2The 

summary of modeled intakes is shown in Table 17. 

Table 17. Summary of Modeled Intakes 

Type of 

Intake Date of Intake Total Intake/ Intake Rate Additional Comments

Acute 3/27/[redact] 4.5E+03 dpm Only considers the sample taken on 3/27/[redact].

Acute 3/27/[redact] 1.3E+04 dpm

Only considers the samples taken on 3/31/[redact] and 

4/1/[redact] and ignores the results on 3/27/[redact] and 

3/28/[redact].

Acute 3/27/[redact]

7.86E+03 ± 

77.9% dpm Utilizes the “Point Estimate” method of bioassay fitting.

Acute 3/27/[redact] 1.5E+03 dpm Utilizes the unweighted least squares fit method.

ORAUT 2013 assigns a Cm-244 coworker intake of 19.3 dpm/d, which results in a total annual 

intake of 7,044 dpm. This value is compatible with the point estimate calculated intake rate 

based on the acute incident intake (7,860 dpm), which was the most claimant-favorable 

calculated intake based on all four results. The highest modeled acute intake (13,000 dpm) is a 

factor of 2 higher than the 95th percentile coworker intakes; however, this is deemed acceptable 

considering the error associated with discarding the samples on the 27th and 28th

.

 

2

 ICRP Publication 23 (1975) reports 1.4 liters as the daily excretion rate, while ICRP Publication 89 

(2001) reports 1.6 liters as the daily excretion rate. 
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Figure 12. Incident Report for Cm-244 Intake Occurring on 3/27/[redact]

7.1.2 Additional Comments 

One particularly difficult challenge in calculating hypothetical intake scenarios based on the 

documented incident is the quality of the available monitoring data. As noted in Table 16, the 

NOCTS bioassay records do not agree with the logbook results (either “raw” or “report” results) 
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on March 27 and March 28. Most significant is that the NOCTS records contain measurements 

on both March 27 and March 28 of 50 dpm/1.5 L (see Figure 13).

Figure 13. Bioassay Record Located in Claimant’s NOCTS File

The logbook results for this worker and dates in question are shown in Figures 14–15. As seen 

in Figure 14, the results were clearly called into question by the laboratory and the report 

indicates “Do Not Report.” These results were included in the coworker model database. The 

original logbook record also contains the notation, “See Page 165, 4-15-75 Am” (not shown in 

Figure 14). “Page 165” is shown in Figure 15. 

Figure 14. Logbook Record Showing Results for 3/27 and 3/28. Record indicates 

“Do Not Report”
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Figure 15. Additional Logbook Entries for Claimant Samples on 3/27 and 3/28 

7.1.3 Conclusion 

In summary, the assignment of the 95th percentile coworker intake rate on an annual basis is 

comparable to the calculated acute intake based on the four post-accident bioassay samples 

taken. However, SC&A noted significant data quality issues, which make an accurate estimate 

on intake difficult to obtain. 

7.2 CLAIM #[1]

Employment Period: [Redacted]–[Redacted]

Job Title: [Redacted]

Table 18 displays the claimant’s trivalent bioassay sampling during the SEC period. No 

indication of any incident preceding the positive sample on January 27, [redact], was identified; 

however, the sample taken on the preceding day was designated as “special.” 

Table 18. Trivalent Urinalysis Results during SEC Period for Claim #[1]

Date

Bioassay Value (dpm/1.5L)

Database Additional Comments

Result(s)

Logbook 

Report 

Value

NOCTS 

Result

1/26/[redact]

0.435, 0, 

0.049 <0.3 <0.3 Sample Designation: “Special”, special in vivo count also conducted on this day with no positive result.

1/27/[redact]

0.479, 0.594, 

0.511, 1 0.6 0.6 Sample Designation: “Follow-up”

5/14/[redact] Missing Missing <0.3

4/30/[redact] -0.151 <0.3 <0.3

12/14/[redact] Missing Missing <0.3

4/29/[redact] 0.217 <0.3 <0.3

5/12/[redact] 0.036 <0.3 <0.3

4/27/[redact] -0.022 <0.3 <0.3

5/24/[redact] -0.215 <0.3 <0.3

4/20/[redact] Missing Missing <0.3
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7.2.1 Intake Scenarios Considered 

The samples shown in Table 19 for 1/26 and 1/27/[redact] were labelled “special” and “follow 

up,” respectively. Although no documentation was identified in the file as to what special work 

may have been done or if there was an incident-driven intake, SC&A has assumed that the 

exposure occurred on 1/26 and was first identified in the follow-up sample on 1/27. It should be 

noted that one of the disc results taken on 1/26 was measured as positive (0.435 dpm/d);

however, the overall average was less than the MDA of 0.3 dpm/d.

Table 19. Summary of Modeled Intakes 

Type of 

Intake Date of Intake Total Intake/ Intake Rate Additional Comments

Acute 1/26/[redact] 3.4E+02 dpm Intake assumed to be Am-241

Acute 1/26/[redact] 3.4E+02 dpm Intake assumed to be Cm-244

Acute 1/26/[redact] 4.6E+02 dpm Intake assumed to be Cf-252

7.2.2 Additional Comments 

Based on Table 18, it appears the claimant was on a routine annual monitoring program 

beginning in 1984 with samples collected around April/May of each year. All the results of 

these annual samples were below the DL. The 95th percentile intake rates based on the coworker 

model would predict urinary excretion rates below MDA for Cm and Am in the first 10 years of 

exposure. 

Similar to Case #[3], data quality problems complicate the calculation of accurate intake 

assessments. For example, it can be seen in Table 19 that the day of the assumed intake, the 

claimant submitted a sample that was counted three times. Those results yielded one result 

above the MDA (0.435 dpm/d), 1 result below the MDA (0.049, an order of magnitude lower 

than the first measurement), and one result of zero. Additionally, the positive result on January 

27th was measured five separate times (all of them positive measurements). The results varied by 

over a factor of 2 and ranged from 0.479 dpm/d up to 1 dpm/d.

7.2.3 Conclusion 

The 95th percentile annual coworker intakes are 6,100/7,100/25,000 dpm for Am/Cm/Cf, 

respectively. In each case, the annual 95th percentile coworker intake assignment bounds the 

calculated intake based on an acute exposure on January 26, [redact], as shown in Table 19. 

7.3 CLAIM #[2]

Employment Period: [Redacted]–[Redacted]

Job Title: [Redacted]

Table 20 displays the trivalent bioassay data for the claimant during the SEC period. The only 

positive result was observed on May 18, [redact]; the next sample taken was nearly 3 years later. 

The NOCTS file for this claimant notes three separate contamination incidents; however, none of 

the incidents appears to have resulted in an intake of trivalent actinides. 
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Table 20. Trivalent Urinalysis Results during SEC Period for Claim #[2]

Date

Bioassay Value (dpm/1.5L)

Database Additional Comments

Result(s)

Logbook 

Report 

Value

NOCTS 

Result

2/7/[redact] 0.026 <0.3 <0.3

7/12/[redact] 0 <0.3 <0.3

10/15/[redact] 0 <0.3 <0.3 Sample Designation: “Special”

1/28/[redact] 0 <0.3 <0.3

7/8/[redact] 0 <0.3 <0.3

1/9/[redact] 0.078 <0.3 <0.3

7/8/[redact] 0.06 <0.3 <0.3

1/7/[redact] 0 <0.3 <0.3

7/6/[redact] Missing Missing <0.3

4/11/[redact] 0 <0.3 <0.3

5/18/[redact] 0.371, 0.309 0.3 0.3

3/14/[redact] 0 <0.3 <0.3

10/27/[redact] 0.026 <0.3 <0.3

8/20/[redact] 0 <0.3 <0.3

8/23/[redact] -0.081 <0.3 <0.3

8/7/[redact] -0.037 <0.3 <0.3

7.3.1 Intake Scenarios Considered 

Table 21 summarizes the modeled intakes based on the single observed positive urinalysis 

sample. As seen in Table 21, the predicted excretion result based on the application of the 95th

percentile Am-241 coworker intake rate is approximately 0.23 dpm/d on the day of the observed 

positive sample (reported as 0.3 dpm/d in NOCTS). Additionally, if the positive result is 

assumed to be caused by an acute exposure occurring midway between the positive and previous 

sample, the resulting intake is approximately a factor of 5 larger than the 95th percentile chronic 

coworker assignment over a full year of chronic exposure. 

Table 21. Summary of Calculated Intakes and Intake Comparison 

Type of 

Intake

Date of Intake or 

Duration of Intake

Total Intake 

(dpm) or 

Intake Rate 

(dpm/d) 

Additional Comments

Coworker 

Chronic

1/1/[redact]–

5/18/[redact]

16.7 dpm/d

Intake rate based on 95th percentile coworker Am-241 intake 

rate (ORAUT 2013).

The predicted excretion rate based on the coworker intake rate 

would be 0.23 dpm/d on the date of the positive sample 

(5/18/[redact]).

Acute 10/29/[redact] 3E+04 dpm

Date of intake assumed to be half way between positive 

sample and prior sample (201 days prior to the positive 

sample).

95th percentile coworker intake over the 201-day period totals 

3.36E+03 dpm.
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7.3.2 Conclusion 

Application of the 95th percentile of the coworker model as a chronic exposure beginning in 

[redact] would result in a lower predicted excretion rate than the positive sample observed in the 

claimant’s monitoring records. If an acute exposure is assumed to have occurred at the midpoint 

between the positive sample and the previous sample, the total acute intake is roughly an order of 

magnitude higher than the 95th percentile intake assignment. 

7.4 CLAIM #[4]

Employment Period: [Redacted]–[Redacted]

Job Title: [Redacted]

Table 22 displays the trivalent bioassay data for the claimant during the SEC period. The only 

positive result was observed on January 8, [redact]; the next sample taken was a few months 

later. The sample on July 8, [redact], also contained one disc measurement that was positive; 

however, the other two measurements for that sample were zero. 

Table 22. Trivalent Urinalysis Results during SEC Period for Claim #[4]

Date

Bioassay Value (dpm/1.5L)

Database Additional Comments

Result(s)

Logbook 

Report 

Value

NOCTS 

Result

1/31/[redact] 0 <0.3 <0.3

7/16/[redact] 0 <0.3 <0.3

1/12/[redact] Blank <0.3 <0.3 Date appears as 1/7/[redact] in claimant record

7/9/[redact] 0 <0.3 <0.3 Date appears to be 3/9/[redact] in claimant record

1/10/[redact] 0 <0.3 <0.3

7/9/[redact] 0 <0.3

10/20/[redact] 0.192 <0.3 <0.3

1/8/[redact]

0.076, 

0.746, 

0.295, 0.864

0.5 0.5

4/23/[redact] 0 <0.3 <0.3 Sample Designation: “Resample”

7/8/[redact] 0, 0.337, 0 <0.3 <0.3

1/7/[redact] 0 <0.3 <0.3

1/12/[redact] 0 <0.3 <0.3 Date appears as 1/12/[redact] in claimant record

3/16/[redact] 0 <0.3 <0.3

7.4.1 Intake Scenarios Considered 

Table 23 summarizes the modeled intakes based on the single observed positive urinalysis 

sample. As seen in Table 23, the predicted excretion result based on the application of the 95th

percentile Am-241 coworker intake rate is approximately 0.23 dpm/d on the day of the observed 

positive sample (reported as 0.3 dpm/d in NOCTS). Additionally, if the positive result is 

assumed to be caused by an acute exposure occurring midway between the positive and previous 

sample, the resulting intake is approximately an order of magnitude larger than the 95th

percentile chronic coworker assignment over the same period. 
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Table 23. Summary of Calculated Intakes and Intake Comparison 

Type of 

Intake

Date of Intake or 

Duration of 

Intake

Total Intake 

(dpm) or Intake 

Rate (dpm/d) 

Additional Comments

Coworker 

Chronic

1/1/[redact]–

1/8/[redact]

16.7 dpm/d

Intake rate based on 95th percentile coworker Am-241 intake 

rate (ORAUT 2013).

The predicted excretion rate based on the coworker intake rate 

would be 0.2 dpm/d on the date of the positive sample 

(1/8/[redact]).

Acute 11/29/[redact] 2.2E+04 dpm

Date of intake assumed to be half way between positive 

sample and prior sample (40 days prior to the positive 

sample).

95th percentile coworker intake over a 1 year period totals 

approximately 6E+03 dpm.

7.4.2 Additional Comments 

As can be seen in Table 22, the positive result on January 8, 1976, had highly variable individual 

disc measurements, which varied by over an order of magnitude (0.076 to 0.864 dpm/d). 

Additionally, it was noted that one other sample had a positive disc result (0.337 dpm/d), but was 

reported as <0.3 since the other two measurements were zero. 

7.4.3 Conclusion 

Application of the 95th percentile of the coworker model as a chronic exposure beginning in 

[redact] would result in a lower predicted excretion rate than the positive sample observed in the 

claimant’s monitoring records. If an acute exposure is assumed to have occurred at the midpoint 

between the positive sample and the previous sample (40 days), the total intake is roughly a 

factor of 4 higher than the 95th percentile intake totaled over 1 year. 

7.5 CLAIM #[5]

Employment Period: [Redacted]–[Redacted]

Job Title: [Redacted]

Table 24 displays the trivalent bioassay data for the claimant during the SEC period. The only 

positive result was observed on January 23, [redact]; the next sample was taken roughly 6 

months later on July 25, [redact]. That sample also contained a positive disc measurement; 

however, the other two measurements for that sample were less than the MDA, so the reported 

result was <0.3. None of the claimant’s samples were labelled as “special” or “resample” or 

“follow-up.” Notably, the claimant was monitored twice a year every year from [redact]–

[redact], but not past this timeframe. The claimant was counted via in vivo in [redact] and 

[redact] with results below the MDA. 
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Table 24. Trivalent Urinalysis Results during SEC Period for Claim #[5]

Date

Bioassay Value (dpm/1.5L)

Database Additional Comments

Result(s)

Logbook 

Report 

Value

NOCTS 

Result

2/12/[redact] 0 <0.3 <0.3

7/27/[redact] 0.12 <0.3 <0.3

1/10/[redact] 0 <0.3 <0.3

7/15/[redact] 0 <0.3 <0.3 Date in claim file is 7/22/[redact].

1/23/[redact] 0.272, 0.374 0.3 0.3

7/31/[redact]

0.203, 

0.374, 0.138 <0.3 <0.3

1/15/[redact] 0 <0.3 <0.3

7/15/[redact] 0.14 <0.3 <0.3

1/6/[redact] 0 <0.3 <0.3

7/19/[redact] 0 <0.3 <0.3 Date in claim file is 7/29/[redact]

7.5.1 Intake Scenarios Considered 

Table 25 summarizes the modeled intakes based on the single observed positive urinalysis 

sample. As seen in Table 26, the predicted excretion result based on the application of the 95th

percentile Am-241 coworker intake rate is approximately 0.23 dpm/d on the day of the observed 

positive sample (reported as 0.3 dpm/d in NOCTS). Additionally, if the positive result is 

assumed to be caused by an acute exposure occurring midway between the positive and previous 

sample, the resulting intake is approximately an order of magnitude larger than the 95th

percentile chronic coworker assignment over the same period. 

Table 25. Summary of Calculated Intakes and Intake Comparison 

Type of 

Intake

Date of Intake or 

Duration of Intake

Total Intake 

(dpm) or 

Intake Rate 

(dpm/d) 

Additional Comments

Coworker 

Chronic

1/1/[redact]–

1/23/[redact]

16.7 dpm/d

Intake rate based on 95th percentile coworker Am-241 intake 

rate (ORAUT 2013).

The predicted excretion rate based on the coworker intake rate 

would be 0.18 dpm/d on the date of the positive sample 

(1/23/[redact]).

Acute 10/19/[redact] 2.1E+04 dpm

Date of intake assumed to be half way between positive sample 

and prior sample (40 days prior to the positive sample).

95th percentile coworker intake over a 1 year period totals 

approximately 6E+03 dpm.

7.5.2 Additional Comments 

The claimant’s urine result from January 23, [redact], had an average of 0.32 and was reported 

in the claimant’s NOCTS bioassay file as 0.3 dpm/1.5 L. One problem with the result is its 

inconsistency among the discs that should reflect the same sample activity. There were two disc 

results, one of them less than the MDA (0.272 dpm/1.5 L) and one higher than the MDA 

(0.374/1.5 L). Similarly, the claimant’s urine result from July 31, [redact], had three disc results 

(0.203 dpm/1.5 L, 0.374 dpm/1.5 L and 0.138 dpm/1.5 L). The first two disc results are similar 
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to the ones obtained in January 23, [redact]; however, the third disc showed a much lower 

counting rate. The result from July 31, [redact], was reported as below the MDA. The 

uncertainties on results near or below the MDA are very high; if the claimant was actually 

exposed to Am-Cm during [redact], it is feasible they could have been exposed for the entire 

year.

7.5.3 Conclusion 

Application of the 95th percentile of the coworker model as a chronic exposure beginning in 

[redact] would result in a lower predicted excretion rate than the positive sample observed in the 

claimant’s monitoring records. If an acute exposure is assumed to have occurred at the midpoint 

between the positive sample and the previous sample (96 days), the total intake is a factor of 3–5 

higher than the 95th percentile intake totaled over 1 year. 

7.6 CLAIM #[6]

Employment Period: [Redacted]–[Redacted]

Job Title: [Redacted]/[Redacted]

Table 26 displays the trivalent bioassay data for the claimant during the SEC period. The only 

positive result was observed on June 3, [redact]; the next sample taken was a few months later 

and was designated a “resample.” The positive sample was an average of a disc measurement 

above the MDA and a disc measurement below the MDA. An additional sample on December 

15, [redact], contained one positive disc result; however, the second disc measurement was 

negative, so the sample was reported as <0.3. The claimant was also monitored via in vivo at 

various points from [redact] through [redact]; however, no in vivo result was identified with 

[redact] when the positive bioassay measurement was observed. 

Table 26. Trivalent Urinalysis Results during SEC Period for Claim #[6]

Date

Bioassay Value (dpm/1.5L)

Database Additional Comments

Result(s)

Logbook 

Report 

Value

NOCTS 

Result

6/3/[redact] 0.29, 0.44 0.4 0.4

8/22/[redact] 0 <0.3 <0.3 Sample Designation: “Resample”

12/19/[redact] 0 <0.3 <0.3

6/17/[redact] 0.08 <0.3 <0.3

12/5/[redact] 0 <0.3 <0.3

6/4/[redact] 0 <0.3 <0.3

1/23/[redact] 0 <0.3 <0.3 Date in claim file is 12/23/[redact].

1/3/[redact] 0 <0.3 <0.3

12/12/[redact] -0.056 <0.3 <0.3

12/26/[redact] 0.139 <0.3 <0.3

1/2/[redact] -0.072 <0.3 <0.3

12/15/[redact] 0.323, -0.07 <0.3 <0.3

12/1/[redact] -0.199 <0.3 <0.3

11/30/[redact] 0.1 <0.3 <0.3

12/7/[redact] Missing Missing <0.3
Effective Date:

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7.6.1 Intake Scenarios Considered 

Table 27 summarizes the modeled intakes based on the single observed positive urinalysis 

sample. As seen in Table 27, the predicted excretion result based on the application of the 95th

percentile Am-241 coworker intake rate is approximately 0.15 dpm/d on the day of the observed 

positive sample (reported as 0.4 dpm/d in NOCTS). In order to reach an Am-241 excretion rate 

on the day in question of 0.4 dpm/d, a continuous intake rate of 26 dpm/d would be required 

(higher than the 95th percentile coworker intake of 16.7 dpm/d). Similarly, if the exposure was 

due to Cm-244, a continuous intake rate of 44 dpm/d would be required (higher than the 95th

percentile coworker intake of 19.3 dpm/d). 

If the claimant’s excretion rate were a result of an acute intake, we do not have information on 

the date of the intake. The ICRP recommends the use of the middle of the interval between 

monitoring results as the intake date. Although the claimant had a previous result listed in the 

coworker database for December 7, [redact], this result was “reported” in the original records as 

lost in process. This result does not appear in the NOCTS monitoring records provided by the 

U.S. Department of Energy (DOE). Therefore, it is inappropriate to use this sample to establish 

a reasonable acute intake date and thus there is insufficient information available to estimate an 

acute intake.

Table 27. Summary of Calculated Intakes and Intake Comparison 

Type of 

Intake

Date of Intake or 

Duration of 

Intake

Total Intake 

(dpm) or 

Intake Rate 

(dpm/d) 

Additional Comments

Coworker 

Chronic

1/1/[redact]–

6/3/[redact]

16.7 dpm/d

Intake rate based on 95th percentile coworker Am-241 intake rate 

(ORAUT 2013).

The predicted excretion rate based on the coworker intake rate

would be 0.15 dpm/d on the date of the positive sample 

(6/3/[redact]).

7.6.2 Additional Comments 

As can be seen in Table 26, the positive result on June 3, [redact], consisted of both an above 

MDA measurement (0.44 dpm/d) and a below MDA measurement (0.29 dpm/d). Additionally, it 

was noted that one other sample had a positive disc result (0.323 dpm/d), but was reported as 

<0.3 since the other disc measurement was negative.

7.6.3 Conclusion 

Application of the 95th percentile of the coworker model as a chronic exposure beginning in 

[redact] would result in a lower predicted excretion rate than the positive sample observed in the 

claimant’s monitoring records. If an acute exposure is assumed to have occurred at the midpoint 

between the positive sample and the previous sample (69 days), the total intake is over a factor of 

4 higher than the 95th percentile intake totaled over 1 year. 
Effective Date:

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7.7 CLAIM #[8]

Employment Period: [Redacted]–[Redacted]

Job Title: [Redacted]

Table 28 displays the trivalent bioassay data for the claimant during the SEC period. Two 

positive results were observed on January 15, [redact], and March 8, [redact]; the latter sample 

was designated a “resample.” Both samples consisted of only positive disc results. The claimant 

was also monitored via in vivo in [redact] and had a positive Am-241 result of 0.15 nCi. 

Table 28. Trivalent Urinalysis Results during SEC Period for Claim #[8]

Date

Bioassay Value (dpm/1.5 L)

Database Additional Comments

Result(s)

Logbook 

Report 

Value

NOCTS 

Result

7/11/[redact] 0 <0.3 <0.3

1/8/[redact] 0 <0.3 <0.3

7/15/[redact] 0 <0.3 <0.3

1/24/[redact] 0.175 <0.3 <0.3

7/11/[redact] 0 <0.3 <0.3

1/15/[redact] 0.463, 0.698 0.6 0.6

3/8/[redact] 0.712, 0.579 0.6 0.6 Sample Designation: “Resample”

5/11/[redact] 0 <0.3 <0.3

5/17/[redact] 0 <0.3 <0.3

5/17/[redact] 0 <0.3 <0.3

7/12/[redact] 0, 0.21 <0.3 <0.3

7/18/[redact] 0 <0.3 <0.3

7.7.1 Intake Scenarios Considered 

Table 29 summarizes the modeled intakes based on the single observed positive urinalysis 

sample. As seen in Table 29, the predicted excretion result based on the application of the 95th

percentile Am-241 coworker intake rate is approximately 0.2 dpm/d on the day of the observed 

positive sample (reported as 0.3 dpm/d in NOCTS). The continuous Am-241 intake rate required 

to reach an excretion rate of 0.6 dpm/d is approximately 51 dpm/d (compared to the 95th

percentile coworker assignment of 16.7 dpm/d). Similarly, if the exposure was to curium, the 

observed excretion rate would correspond to a continuous intake rate of 53 dpm/d (compared to 

the 95th percentile coworker assignment of 19.3 dpm/d). 

Additionally, if the positive result is assumed to be caused by an acute exposure occurring 

midway between the positive and previous sample, the resulting intake is approximately an order 

of magnitude larger than the 95th percentile chronic coworker assignment over the same period. 
Effective Date:

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Table 29. Summary of Calculated Intakes and Intake Comparison 

Type of 

Intake

Date of Intake or 

Duration of Intake

Total Intake 

(dpm) or 

Intake Rate 

(dpm/d) 

Additional Comments

Coworker 

Chronic

1/1/[redact]–

1/15/[redact]

16.7 dpm/d

Intake rate based on 95th percentile coworker Am-241 intake 

rate (ORAUT 2013).

The predicted excretion rate based on the coworker intake rate 

would be 0.2 dpm/d on the date of the positive sample 

(1/15/[redact]).

Acute 7/21/[redact] 5.45E+04 dpm

Date of intake assumed to be half way between positive sample 

and prior sample (178 days prior to the positive sample).

95th percentile coworker intake over a 1 year period totals 

approximately 6E+03 dpm.

7.7.2 Conclusion 

Application of the 95th percentile of the coworker model as a chronic exposure beginning in 

[redact] would result in a lower predicted excretion rate than the positive sample observed in the 

claimant’s monitoring records. If an acute exposure is assumed to have occurred at the midpoint 

between the positive sample and the previous sample (178 days), the total intake is nearly an 

order of magnitude higher than the 95th percentile intake totaled over 1 year. 

7.8 CLAIM #[9]

Employment Period: [Redacted]–[Redacted]

Job Title: [Redacted]

Table 30 displays the trivalent bioassay data for the claimant during the SEC period, the claimant 

was also monitored through in-vivo counting in [redact]–[redact], [redact], and [redact]. The 

only positive result was observed on December 28, [redact]; this sample could not be located in 

the NOCTS claimant files. The sample contained three disc measurements that were positive 

and one disc measurement that was zero. The claimant was monitored via in vivo multiple times 

from [redact] up through [redact] (including [redact]); however, all results were less than the 

MDA. 

Table 30. Trivalent Urinalysis Results during SEC Period for Claim #[9]

Date

Bioassay Value (dpm/1.5L)

Database Additional Comments

Result(s)

Logbook 

Report 

Value

NOCTS 

Result

3/16/[redact]

0.18, 0.288, 

0.015 <0.3 <0.3

12/28/[redact]

0.771, 

0.925, 0, 

0.511

0.8 Missing Only a plutonium sample exists on this date in the 

claim file.

12/5/[redact] 0, 0.079 <0.3 <0.3
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7.8.1 Intake Scenarios Considered 

Table 31 summarizes the modeled intakes based on the single observed positive urinalysis 

sample. As seen in Table 31, the predicted excretion result based on the application of the 95th

percentile Am-241 coworker intake rate is approximately 0.23 dpm/d on the day of the observed 

positive sample. The required continuous intake rate of Am-241 to reach 0.8 dpm/d on 

12/28/[redact] would be 58 dpm/d (compared to the 95th percentile coworker assignment of 

16.7 dpm/d). Similarly, if the exposure was due to curium, then the required continuous intake 

rate would be 61 dpm/d (compared to the 95th percentile coworker assignment of 19.3 dpm/d). 

Additionally, if the positive result is assumed to be caused by an acute exposure occurring 

midway between the positive and previous samples, the resulting intake is approximately an 

order of magnitude larger than the 95th percentile chronic coworker assignment for a full year of 

exposure. 

Table 31. Summary of Calculated Intakes and Intake Comparison 

Type of 

Intake

Date of Intake or 

Duration of Intake

Total Intake 

(dpm) or 

Intake Rate 

(dpm/d) 

Additional Comments

Coworker 

Chronic

1/1/[redact]–

12/28/[redact]

0.23 dpm/d

Intake rate based on 95th percentile coworker Am-241 intake 

rate (ORAUT 2013).

The predicted excretion rate based on the coworker intake 

rate would be 0.23 dpm/d on the date of the positive sample 

(12/28/[redact]).

Acute 8/6/[redact] 6.5E+04 dpm

Date of intake assumed to be halfway between positive 

sample and prior sample (144 days prior to the positive 

sample).

95th percentile coworker intake over a 1 year period totals 

approximately 6E+03 dpm.

7.8.2 Additional Comments 

As can be seen in Table 30, the positive result on December 28, [redact], had highly variable 

individual disc measurements, which ranged from zero to 0.925 dpm/d. Three of the four disc 

measurements were well above the MDA (0.511, 0.711, 0.925 dpm/d), while the fourth was zero.

7.8.3 Conclusion 

Application of the 95th percentile of the coworker model as a chronic exposure beginning in 

[redact] would result in a lower predicted excretion rate than the positive sample observed in the 

claimant’s monitoring records. If an acute exposure is assumed to have occurred at the midpoint 

between the positive sample and the previous sample (144 days), the total intake is over an order 

of magnitude higher than the 95th percentile intake totaled over 1 year. 
Effective Date:

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However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker 

Health for factual accuracy or applicability within the requirements of 42 CFR 82. 

7.9 CLAIM #[10]

Employment Period: [Redacted]–[Redacted]

Job Title: [Redacted]/[Redacted]

Table 32 displays the trivalent bioassay data for the claimant during the SEC period. The only 

positive result in the coworker database was observed on January 11, [redact]; the next sample 

was taken nearly a year and a half later. The positive sample consisted of three disc results that 

were all above the MDA of 0.3. In the NOCTS claim file, the positive result of “0.4 dpm/d” was 

taken on August 30, [redact]. The claimant also had several in-vivo monitoring results from 

[redact] to [redact]. All measured results were below the MDA, although no in-vivo 

monitoring results were available in [redact].

Table 32. Trivalent Urinalysis Results during SEC Period for Claim #[10]

Date

Bioassay Value (dpm/1.5L)

Database Additional Comments

Result(s)

Logbook 

Report 

Value

NOCTS 

Result

1/11/[redact] 0.002 <0.3 Missing No bioassay results were identified in [redact] in claim 

file.

1/11/[redact]

0.353, 

0.506, 0.34 0.4 <0.3

8/30/[redact] Missing Missing 0.4

6/28/[redact] 0 <0.3 <0.3

3/8/[redact] Missing Missing <0.3

3/4/[redact] 0.002 <0.3 <0.3

7.9.1 Intake Scenarios Considered 

Table 33 summarizes the modeled intakes based on the single observed positive urinalysis 

sample. As seen in Table 33, the predicted excretion result based on the application of the 95th

percentile Am-241 coworker intake rate is approximately 0.24 dpm/d on the day of the observed 

positive sample (reported as 0.4 dpm/d in NOCTS). The Am-241 continuous intake rate required 

to obtain the observed positive result in 1979 would by approximately 28 dpm/d (compared to 

the 95th percentile coworker model intake rate of 16.7 dpm/d). If the exposure were attributed to 

curium, a continuous intake rate of 0.29 dpm/d would be required (higher than the 95th percentile 

coworker intake rate of 19.3 dpm/d). 

Table 33. Summary of Calculated Intakes and Intake Comparison 

Type of 

Intake

Date of Intake or 

Duration of Intake

Total Intake 

(dpm) or 

Intake Rate 

(dpm/d) 

Additional Comments

Coworker 

Chronic

1/1/[redact]–

1/11/[redact]

0.24 dpm/d

Intake rate based on 95th percentile coworker Am-241 intake rate 

(ORAUT 2013).

The predicted excretion rate based on the coworker intake rate 

would be 0.24 dpm/d on the date of the positive sample 

(1/11/[redact]).
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7.9.2 Conclusion 

Application of the 95th percentile of the coworker model as a chronic exposure beginning in 

[redact] would result in a lower predicted excretion rate than the positive sample observed in the 

claimant’s monitoring records. The continuous intake rate required to obtain the observed 

positive result exceeds the 95th percentile coworker intake for americium and curium. 

7.10 CLAIM #[12]

Employment Period: [Redacted]–[Redacted], [Redacted]–[Redacted]

Job Title: [Redacted]

Table 34 displays the trivalent bioassay data for the claimant during the SEC period. The only 

positive result was observed on April 29, [redact], with additional samples taken in subsequent 

days. The sample contained one disc measurement that was positive and one disc measurement 

that was below the MDA. The claimant was involved in an Am-241 intake incident that 

occurred during a maintenance operation. In addition to the bioassay results shown, fecal and invivo monitoring were also conducted. These monitoring results are presented and discussed 

under “Intake Scenarios Considered.” 

Table 34. Trivalent Urinalysis Results during SEC Period for Claim #[12]

Date

Bioassay Value (dpm/1.5 L)

Database Additional Comments

Result(s)

Logbook 

Report 

Value

NOCTS 

Result

4/29/[redact] 0.679, 0.223 0.4 0.4 Sample Designation: “Special”

5/1/[redact] 0.164 <0.3 <0.3 Sample Designation: “Follow-up”

5/2/[redact]

0, 0.552, 0, 

0.161

<0.3 <0.3 Sample Designation: “Follow-up”

5/2/[redact]

0, 0, 0.147, 

1.92 <0.3 <0.3

The average of the disc results is 0.52 dpm/d; however,

the logbook and NOCTS files report the value as <0.3. 

The coworker database uses the average value. It 

appears that the 1.92 dpm/d disc result was crossed out 

in the original hardcopy record.

5/5/[redact]

0.223, 

0.343, 

0.211, 0.204

<0.3 <0.3 Sample Designation: “Follow-up”

7.10.1 Intake Scenarios Considered 

The in-vivo and fecal monitoring results are presented in Tables 35 and 36, respectively. Based 

on these results, it appears that the available bioassay measurements do not adequately reflect the 

actual intake experienced by the claimant. Using the five positive in-vivo results and the 

unweighted least squares method, the calculated acute intake is approximately 16 nCi 

(3.6E+04 dpm). This calculated acute intake is higher than the annual Am-241 assignment at the 

95th percentile (6E+03 dpm per year). 
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Table 35. In-Vivo Monitoring Results for Claim #[12]

Date Days Post 

Intake

Measured 

Contaminant Results (nCi)

4/30/[redact] 1

Am-241 1.21

Cm-244 51

Pu-239 97

Pu-238 41

5/5/[redact] 6

Am-241 0.53

Cm-244, Pu-239, 

Pu-238 <MDA

10/21/[redact] 175

Am-241 0.29

Cm-244, Pu-239, 

Pu-238 <MDA

1/26/[redact] 272 Am-241 <0.16

5/19/[redact] 385 Am-241 <0.19

9/2/[redact] 491 Am-241 0.17

5/16/[redact] 747 Am-241 0.17

Table 36. Fecal Sampling Results for Claim #[12]

Date Activity 

(nCi) Mass Daily Excretiona(nCi/d)

5/1/[redact] 0.4 54 1.1

5/3/[redact] 2.3 140 2.4

5/4/[redact] <0.2 36 –

5/5/[redact] <0.3 36 –

a ICRP Publication 89 (2002) assumes the daily mass of fecal 

excretion for a reference male is 150 grams. 

The fecal results shown in Table 36 carry a lot of uncertainty related to the amount excreted per 

day and the daily function of the intestinal tract. This may account for the increase in the activity 

excreted in feces from May 1, [redact], to May 4, [redact]. Despite these uncertainties, it can be 

concluded that a significant activity of Am-241 was inhaled by the worker. Another very 

important conclusion from this case is that the urine activity excreted did not reflect the intake of 

this worker. The reported result would predict an intake of 2.3E+02 dpm, much lower than the 

one predicted by the available chest count. It must also be noted that one of the two disc results 

used to indicate the intake of the worker was below the MDA. 

7.10.2 Conclusion 

Based on the in-vivo and fecal sampling for the claimant, as well as the documented intake of 

Am-241 on April 29, [redact], it is evident that the associated urinalysis measurements did not 

adequately identify the significant acute intake experienced by the worker. Furthermore, the 95th

percentile coworker intake rate would underestimate the observed excretion rate if continuous 

exposure is assumed beginning in [redact] and extending through the date of the positive 

sample. 
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7.10.3 Intake Analysis Findings 

Finding 17: Uncertainties observed in the urine in-vitro methodology are very high for the 

sampled claimants, making accurate intake assessments particularly difficult. This is evident in 

multiple instances where differences in disc results for the same sample are significant. 

Additionally, the reported urinalysis activity was very low for one claimant who had a confirmed 

high intake based on fecal and in vivo measurements. This may be due to problems in the urine 

bioassay method. 

Finding 18: The 95th percentile daily intake rates for Am-241 and Cm-244 in the period 1973–

1994 predict excretion rates that are below the DL for the first 10 years of continuous exposure. 

Any worker that had a positive excretion rate during the first 10 years of exposure without an 

indication of a specific incident occurring in a small interval of time before the sampling will be 

misrepresented by the 95th percentile coworker model. 
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8.0 EVALUATION OF THE COMPLETENESS OF THE 

TRIVALENT ACTINIDE BIOASSAY DATABASE 

In order to assess the completeness of the compiled trivalent actinide bioassay data, SC&A 

analyzed the job title (Section 8.1) and work location (Section 8.2) included with each result. In 

addition, SC&A examined the NOCTS files for any claimant contained in the database. This 

analysis included verifying the job title classification as well as comparing the monitoring results 

provided by DOE to the compiled results used in the coworker model (Section 8.3). The 

database itself is located at: [O:\Savannah River Site SEC\SRS databases for Coworker Models 

021713\Am Final Compiled_SRS WHC_06302011r2_OPOS analysis R10 CTW NCW unkstrata 

%s.xlsx]. For this analysis, SC&A only considered records taken from October 1972 through 

December 1989. 

Observation 1: SC&A noted that many results were excluded from the OPOS analysis for 

various reasons including no apparent date to the sample, sample was marked lost in process, or 

chelation was involved. SC&A identified 52 samples that were excluded, mainly based on a 

missing date, which likely could still be used in the coworker model since the date of the report 

can be used to accurately place the sample in a given year. 

8.1 ANALYSIS OF MONITORED JOB TITLES 

Job titles were originally assessed in RPRT-0055 by two main methods, as described in 

Section 3.2 of that report. Namely, occupations were assigned based on either a payroll ID 

prefix or using a specific employee’s “SRS Work History Card.” SC&A was not able to review 

the latter source of employment information, as the original directory containing that information 

is not available. However, SC&A was able to compare job classification information involving 

claimants which is discussed in Section 8.3. Nonetheless, SC&A evaluated the assigned job 

titles in the database population to assess which occupations were selected for monitoring. 

The dataset contains over 50 distinct job titles. In order to simplify the analysis, SC&A 

combined several job types into nine individual categories shown as “SC&A Condensed Job 

Title” in column 1 of Table 37. The second column of Table 37 displays the number of bioassay 

results associated with each job category, and also the percentage of total samples for each 

occupation. For clarification, column 3 indicates which unique job titles were associated with 

the larger category. For example, one can see that the “Technician/Operator” category contains 

3,076 total samples covering 7 individual job titles, 1,698 of which are attributed to the job title 

of “Technical Assistant.” 

Not surprisingly, the most samples were attributed to the “Technician/Operator” category,

followed by “Trade Workers” and “Scientists/Engineers.” It is logical that these types of 

occupations would have the higher exposure potential and indicates that the sampling protocol 

was not homogeneous. This is reinforced by the fact that administrative-type positions 

composed only about 1% of the available samples. 
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Table 37. Overview of Job Titles by Sample Present in Am/Cm/Cf Database during the 

SEC Period 

SC&A Condensed 

Job Title

Total Samples 

(% of Total)

Database Job Titles Included in Condensed Category

(Number of Samples)

Technician/Operator 3,076 (36.26%)

Technical Assistant (1,698), Operator (1,111), Technician (238), 

Power Operator (15), Lab (7), Lab analyst (4), Heavy Water 

Operator (3) 

Trade Worker 1,421 (16.75%)

Mechanic (940), Electrician (266), Laborer (65), Pipefitter (37),

Sheetmetal Worker (35), Heavy Equipment Operator (22), 

CTW (15), Painter (15), Boilermaker (7), Maintenance (7), 

Rigger (5), Carpenter (4), Millwright (2), Ironworker (1)

Scientist/Engineer 1,301 (15.34%)

Engineer (569), Chemist (535), Research Associate (66), 

Metallurgist (56), Physicist (44), Ceramist (13), Geologist (12), 

Biologist (4), Mathematician (1)

Supervisor/Foreman 1,083 (12.77%) Supervisor (655), Foreman (407), Laboratory Supv (11), 

Manager (9), Shift Supervisor (1)

Unknown 662 (7.80%) “Unk” (265), Roll 2 (223), Roll 1 (174), Blank

Health Physics 586 (6.91%) Health Physics (586)

Project Assistant 132 (1.56%) Project Assistant (113), Assistant (19)

Other 131 (1.54%)

Co-op (28), Glass Blower (22), Patrolman (22), Driver (17), 

Specialist (13), Draftsman (9), Fellow (7), Computer (5), 

Illustrator (5), Conductor (1), Librarian (1), Photographer (1)

Administrative 91 (1.07%) Clerical (90), Accountant (1)

Table 38 further analyzes the assigned job titles by examining the number of individual workers 

monitored, as opposed to the total number of samples. Similar to Table 37, the “Technician/ 

Operator” category made up the largest portion of monitored workers and also had the second 

highest average number of samples per worker. It is also worth noting that administrative-type 

positions had the lowest average number of samples per worker. 

Table 38. Overview of Job Titles by Worker in the Am/Cm/Cf Database 

during the SEC Period 

SC&A Condensed Job Title Number of Workers 

(% of Total)

Average Number of 

Samples per Worker

Technician/Operator 547 (28.76%) 5.62

Scientist/Engineer 308 (16.19%) 4.22

Trades Worker 306 (16.09%) 4.64

Supervisor/Foreman 263 (13.83%) 4.12

Unknown 263 (13.83%) 2.52

Health Physics 72 (3.79%) 8.14

Other 67 (3.52%) 1.96

Administrative 47 (2.47%) 1.94

Project Assistant 29 (1.52%) 4.55

Observation 2: Based on the job title analysis, it is apparent that the monitored worker 

population is not homogeneous but biased towards job types that are more likely to be exposed, 

such as lab technicians/technical assistants and operators. 
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8.2 ANALYSIS OF ASSOCIATED WORK AREAS 

In addition to job title, the work areas associated with each individual sample were examined to 

establish the focus of the monitoring program. Similar to the job title analysis, SC&A condensed 

the 32 distinct locations contained in the database to 11 main work areas, as shown in Table 39. 

By far, the most common area sampled was the “Laboratory/Technology Areas,” which 

comprised nearly three quarters of the dataset. The subset of this condensed area is focused on 

Building 773 (also known as the Savannah River Laboratory), where the majority of exposure 

potential to trivalent actinides is likely to occur. The Separations Facilities (F and H area) are 

next highest. The “Central Shops” were rarely reported as the work location. However, as noted 

in the previous section, “Trades Workers” comprised a significant portion of the monitored 

population, so it is likely this is simply an indication of where the employee was actually 

working versus where they were commonly “badged.”3

Table 39. Overview of Work Areas by Samples Present in Am/Cm/Cf Database 

during the SEC Period 

SC&A Condensed 

Work Areas

Total Samples 

(% of Total)

Database Work Areas Included in Condensed Category 

(Number of Samples)

Laboratory/Technology 

Areas 6,196 (73.04%) 773 (4447), A (1287), Tech (225), SRL (120), 773-A (49), 735 (37), 735-A (10), A-773 (10), 793 (8), 7, (2), 703-A (1)

F Area 1,283 (15.12%) F (1282), F-NF (1)

H Area 276 (3.25%) H (276)

Reactors 253 (2.98%) P (175), C (57), K (19), L (2)

Unknown 222 (2.62%) Blank (217), UNK (5)

CMX/TNX 93 (1.10%) CMX (68), TNX (25)

M Area 55 (0.65%) M (55)

D Area 44 (0.52%) D (44)

G Areas 33 (0.39%) G (33)

Other 18 (0.21%) S (9), NF (6), RR (2), BG(1)

Central Shops 10 (0.12%) CS (8), Crs (1), C/S (1)

Observation 3: The monitoring program is heavily focused on Building 773 (the Savannah 

River Laboratory) where research campaigns were conducted using trivalent actinides and the 

highest potential for intake would likely occur. 

8.3 REVIEW OF CLAIMANT FILES CONTAINED IN THE COWORKER 

DATABASE

Among the monitored worker population, 152 claimants were identified that comprised over 

1,500 of the nearly 8,500 samples (~18%). To establish consistency and completeness of the 

coworker database, the monitoring records provided by DOE for each claimant were compared. 

As noted in Table 40, discrepancies between the database and claimant records fell into three 

categories: 

 

3

 It has been observed that occupations such as maintenance workers often received their external 

dosimetry badges out of the central shops, but would then be assigned to work in various locations at the SRS as 

needed. 
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(1) Records found in DOE claimant files that were not found in the coworker database. 

(2) Records found in the coworker database, but not found in the individual claimant files. 

(3) Records that displayed the same date, but a different year (an example would be the 

database showing 11/1/1981 and the DOE claimant file showing (11/1/1982). 

This third category is important, since the OPOS statistic and subsequent comparison of 

occupational strata are generally based on yearly intervals; therefore, the correct assignment of 

samples to a given year is critical. As can be seen in Table 40, neither source of monitoring 

records could be considered strictly complete, since each contained records that its counterpart 

did not. Logically, one would ask the question of what effect the additional records observed in 

the claimant files would have on the coworker model. With the exception of 5 of the 106 

samples, all of the additional claimant records were below the DL of 0.3 dpm/1.5 L (~ 95% 

<MDA). Conversely, 73 of the 84 samples contained in the coworker database that were not 

found in the claimant records were below the DL (~87% <MDA). Observed instances of a 

discrepancy in the year of a sample (category 3) were approximately 1.9%, which is comparable 

to the 1% critical error rate described in Section 3.1 of RPRT-0055. It should also be noted that 

SC&A identified 80 samples that were taken during or in the months following administration of 

a chelating agent. Per the methodology outlined in Section 3.1 of RPRT-0055, these samples 

should be removed from the coworker dataset. 

Table 40. Summary of Observed Discrepancies between Claimant Monitoring Records 

and Trivalent Coworker Database 

Category 

#

Description Number of 

Observations

Percentage of Total 

Claimant Records

1 Additional Records in Claim File 106 7.0%

2 Additional Records in Coworker Database 84 5.6%

3 Discrepancies in the Year of the Sample 29 1.9%

In addition to the comparison with DOE monitoring records, the claimant files were used to 

compare the job types assigned in NOCTS and described in the claimant’s associated CATI 

reports (Computer Assisted Telephone Interview) to the job assigned in the coworker database. 

In particular, job designations were examined to establish if the worker and associated sample 

were correctly assigned to the “CTW” or “NCW” categories for the purpose of strata 

comparison. In total, 21 of the 152 (~14%) claimants showed some discrepancy between the 

coworker database occupation assignment and what was contained in the individual claim file. 

The specific cases and subsequent investigatory notes are shown in Table 41. Of the 21 

observed cases: 

 14 likely merit a change in job type designation (~9% of all monitored claimants) 

 3 do not merit a change in job designation based on additional information in the claim 

file 

 4 were inconclusive when examining the claim files to establish job category 

As noted previously, SC&A did not have access to the “SRS Work History Cards” that were 

used to establish a given occupation for a worker in a given time period, so we cannot comment 
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on the veracity of that information. However, it is understood that in some of the observed cases 

(particularly the inconclusive cases), the discrepancy could be a product of the fact that often 

occupational information in the claim file is not temporally delineated. Therefore, it may be that 

a claimant began work at SRS in a “CTW” type job and then moved to an “NCW” occupation 

and vice versa. Nevertheless, it would be beneficial for NIOSH to characterize the accuracy of 

the information provided in the “SRS Work History Cards” and, to the extent feasible, perform 

an extensive quality assurance study to verify that workers are correctly assigned to the given 

strata. 
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Table 41. Discrepancies Identified between Coworker Database Occupation Assignment and 

Claimant NOCTS/CATI Job Descriptions

NIOSH 

Claim 

ID

# 

Samples CTW NIOSH Occupation

NOCTS Job 

Title CATI Job Title Additional Comments/Recommended Status Change

[redact] 19 N Roll 1 Mechanic and 

Foreman [redact]

From CATI: “[redact] employees in the E&I Mechanics Group.” 

Recommend change to CTW: “Y”

[redact] 1 Unk Roll 2 Lab Technician [redact] Recommend change to CTW: “N”

[redact] 64 N

Health 

Physics Construction [redact]

CATI report indicates construction work only occurred in the pre1972 timeframe.

Recommend no change.

[redact] 5 N

Project 

Assistant Machinist [redact]

From CATI: “Description of Routine Duties: [redact].” 

Recommend change to CTW: “Y”

[redact] 4 N Foreman Maintenance 

Worker [redact]

From CATI: “Description of Routine Duties: [redact].” 

Recommend change to CTW: “Y”

[redact] 3 N

Project 

Assistant

Instrument 

Mechanic, 

Project 

Assistant

[redact]

From CATI: “Description of Routine Duties: [redact]Unclear when 

claimant moved to reactor operation. DOL form EE-3 lists “E+I 

[redact]” as Position Title and Work Performed. Job designation 

discrepancy is inconclusive.

[redact] 3 N Foreman Mechanic, 

Supervisor [redact]

From CATI: “Description of Routine Duties: [redact].” 

Recommend change to CTW: “Y”

[redact] 1 N Technician

Lab Tech, 

Electrician/ 

Instrument 

Mechanic

[redact]

CATI report does not indicate when job types may have changed. 

DOL file indicates claimant was transferred from [redact] to the E&I 

department as a [redact] but not when it occurred.

Job designation discrepancy is inconclusive.

[redact] 2 N

Project 

Assistant

Area 

Maintenance 

Mechanic

[redact]

From CATI: “[redact].” Actinide samples taken in [redact] and 

[redact].

Recommend no change.

[redact] 5 N Foreman E&I Works 

Engineering [redact]

From CATI: “Duties: [redact].”

Recommend change to CTW: “Y”

[redact] 7 N Roll 1 Maintenance 

Mechanic [redact]

From CATI: “[redact].” Actinide samples cover period when 

claimant was a [redact]. 

Recommend change to CTW: “Y”

[redact] 17 N

Technical 

Assistant

Construction, 

Lab Tech Unavailable

DOL case files do not specify when jobs were changed; however, it 

does indicate the claimant started in [redact] before being hired by 

Du Pont.

Recommend no change.
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Table 41. Discrepancies Identified between Coworker Database Occupation Assignment and 

Claimant NOCTS/CATI Job Descriptions

NIOSH 

Claim 

ID

# 

Samples CTW NIOSH Occupation

NOCTS Job 

Title CATI Job Title Additional Comments/Recommended Status Change

[redact] 1 N Foreman Unavailable [redact]

From CATI: “[redact].”

Recommend change to CTW: “Y”

[redact] 2 N Foreman Maintenance 

Mechanic [redact]

From CATI: “[redact].” No mention of being a foreman found in 

CATI report.

Recommend change to CTW: “Y”

[redact] 4 N

Project 

Assistant

Welder [redact]

From CATI: “Duties: [redact].”

Recommend change to CTW: “Y”

[redact] 8 N Foreman

Machinist, 

Later 

Supervisor

[redact]

From CATI: “[redact].”

Recommend change to CTW: “Y”

[redact] 2 Y Electrician Separations 

Operator [redact]

DOL case file indicates “[redact]” as the work category for this 

claimant.

Recommend change to CTW: “N”

[redact] 6 Y Glass Blower Scientific Glass 

Blower [redact]

Unclear whether this occupation should be included with construction 

trades workers.

Recommend change to CTW: “N”

[redact] 2 N Operator

Laborer, Lab 

Tech, Operator, 

Mechanic

Unavailable DOL lists occupations as: [redact], but does not delineate by period.

Job Designation discrepancy is inconclusive.

[redact] 2 N

Project 

Assistant E&I Mechanic Unavailable From DOL initial case: “[redact].”Recommend change to CTW: “Y”

[redact] 6 N Operator

Laborer, 

General Service 

Operator

[redact]

CATI report lists “unknown” for routine duties.

DOL initial case lists the following job titles: 

[redact]): 

[redact]: 

[redact]:

[redact]:

[redact]

Job Designation discrepancy is inconclusive.
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Observation 4: When comparing the coworker database and individual claimant records, 

neither source appears to be complete. However, the additional records found in the claimant 

files had less positive results than the additional records found in the coworker database. 

Therefore, one can conclude that the samples missing from the coworker database do not 

adversely affect the formulation of a coworker model. 

Observation 5: Approximately 1.9% of the claimant samples reviewed showed discrepancies in 

the year of the sample. While this would be considered a “critical error” in the transcription of 

the data, it is very comparable to the critical error rate of 1% described by NIOSH in Section 3.1 

of RPRT-0055. 

Observation 6: SC&A observed 80 claimant samples that were taken during or in the 

subsequent months following chelation treatment. These samples should be removed from the 

coworker dataset. 

Observation 7: SC&A noted that about 9% of the monitored claimants showed discrepancies 

between the job classifications displayed in the coworker database versus available 

NIOSH/OCAS Claims Tracking System (NOCTS) records. It would be beneficial to perform a 

detailed characterization of how job titles have been established in the coworker database. To 

the extent feasible, an adequate quality assurance activity should be undertaken to ensure that 

monitored workers are correctly placed in the CTW and NCW strata.
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REFERENCES 

ABRWH 2014a. Transcript of the Savannah River Site Work Group – Wednesday, February 5, 

2014. Advisory Board on Radiation and Worker Health. U.S. Department of Health and Human 

Services, Centers for Disease Control, National Institute of Occupational Safety and Health. 

February 5, 2014. 

ABRWH 2014b. Transcript of the Savannah River Site Work Group – Wednesday, February 

26, 2014. Advisory Board on Radiation and Worker Health. U.S. Department of Health and 

Human Services, Centers for Disease Control, National Institute of Occupational Safety and 

Health. February 26, 2014. 

ANSI 1996. Performance Criteria for Radiobioassay. Health Physics Society - American 

National Standards Institute. ANSI N13.30-1996. 

ANSI 2011. Performance Criteria for Radiobioassay. Health Physics Society – American 

National Standards Institute. ANSI N13.30-2011. 

Castellani, C.M., J.W. Marsh, C. Hurgen, E. Blanchardon, P. Berard, A. Giussani, and M.A. 

Lopez 2013. IDEAS Guidelines (Version 2) for the Estimation of Committed Doses from 

Incorporation Monitoring Data, EURADOS Report 2013-01, 2013 (ISSN 22268057, ISBN 978-

3-943701-03-6). 

DCAS 2012. SEC Petition Evaluation Report Petition SEC-00103 Addendum 3. Division of 

Compensation Analysis and Support – National Institute for Occupational Safety and Health. 

November 20, 2012. 

Etherington G., C. Cossonet, D. Franck, J.L. Genicot, C. Hurten, J-R. Jourdan, B. Le Guen, T. 

Rahola, G.N. Stradling, E. Ansoborlo, and P. Berard 2004. Optimization of Monitoring for 

Internal Exposure (OMINEX),NRPB- W60, 2004 (ISBN 0 85951 9).

Hurtgen, C. and C. Cossonnet, 2003. ”A Survey on Uncertainty in Bioassay Measurements 

Carried Out within the OMINEX Project.” Radiation Protection. Dosimetry 105(1–4), 375–

378. 2003.

ICRP 1975. Report on the Task Group on Reference Man. ICRP Publication 23. International 

Commission on Radiological Protection. 1975.

ICRP 1995. Age-Dependent Doses to Members of the Public from Intake of Radionuclides –

Part 4 Inhalation Dose Coefficients. ICRP Publication 71. International Commission on 

Radiological Protection.

ICRP 1997. Individual Monitoring for Internal Exposure of Workers. ICRP Publication 78. 

International Commission on Radiological Protection. 1997.
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However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker 

Health for factual accuracy or applicability within the requirements of 42 CFR 82. 

ICRP 2001. Database of Dose Coefficients: Workers and Members of the Public – Free 

Educational CD Downloads. Supports ICRP Publication 72. International Commission on 

Radiological Protection. 2001.

ICRP 2002. Basic Anatomical and Physiological Data for Use in Radiological Protection 

Reference Values. ICRP Publication 89. International Commission on Radiological Protection. 

2002.

ISO 2006. Radiation Protection -- Monitoring of Workers Occupationally Exposed to a Risk of 

Internal Contamination with Radioactive Material. ISO International Standard 20553:2006, 

International Organization for Standardization, Geneva, 2006.

NCRP 2009. Uncertainties in Internal Radiation Dose Assessment. NCRP Report No. 164. 

National Council on Radiation Protection and Measurements. 2009.

ORAUT 2012a. A Comparison of Exotic Trivalent Radionuclide Coworker Models at the 

Savannah River Site, ORAUT-RPRT-0055, Rev. 00, Oak Ridge Associated Universities Team, 

Cincinnati, Ohio. July 20, 2012. 

ORAUT 2012b. Analysis of Stratified Coworker Datasets, ORAUT-RPRT-0053, Rev. 01, Oak 

Ridge Associated Universities Team, Cincinnati, Ohio. July 16, 2012. 

ORAUT 2013. Internal Coworker Dosimetry Data for the Savannah River Site. ORAUTOTIB-0081 Rev. 02. Oak Ridge Associated Universities Team. Cincinnati, Ohio. December 

16, 2013. 

SC&A 2013. SC&A Review of Addendum 3 to the NIOSH Savannah River Site Special Exposure 

Cohort (SEC-00103) Evaluation Report, S. Cohen & Associates, Vienna, Virginia, and Saliant, 

Inc., Jefferson, Maryland. September 2013. 
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ATTACHMENT A: COMPARISON OF NCW AND CTW 

DISTRIBUTIONS AND GEOMETRIC MEANS, 1966 TO 1989 
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Figure A-1. Comparison of NCW and CTW Distributions and Geometric Means (GM), 

1966–1968 

Figure A-2. Comparison of NCW and CTW Distributions and Geometric Means (GM), 

1969
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Figure A-3. Comparison of NCW and CTW Distributions and Geometric Means (GM), 

1970

Figure A-4. Comparison of NCW and CTW Distributions and Geometric Means (GM), 

1971
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Figure A-5. Comparison of NCW and CTW Distributions and Geometric Means (GM), 

1972

Figure A-6. Comparison of NCW and CTW Distributions and Geometric Means (GM), 

1973
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Figure A-7. Comparison of NCW and CTW Distributions and Geometric Means (GM), 

1974

Figure A-8. Comparison of NCW and CTW Distributions and Geometric Means (GM), 

1975
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Figure A-9. Comparison of NCW and CTW Distributions and Geometric Means (GM), 

1976

Figure A-10. Comparison of NCW and CTW Distributions and Geometric Means (GM), 

1977
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Figure A-11. Comparison of NCW and CTW Distributions and Geometric Means (GM), 

1978

Figure A-12. Comparison of NCW and CTW Distributions and Geometric Means (GM), 

1979
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Figure A-13. Comparison of NCW and CTW Distributions and Geometric Means (GM), 

1980

Figure A-14. Comparison of NCW and CTW Distributions and Geometric Mean (GM), 

1981–1982 
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Figure A-15. Comparison of NCW and CTW Distributions and Geometric Means (GM), 

1983

Figure A-16. Comparison of NCW and CTW Distributions and Geometric Means (GM), 

1984
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Figure A-17. Comparison of NCW and CTW Distributions and Geometric Means (GM), 

1985

Figure A-18. Comparison of NCW and CTW Distributions and Geometric Means (GM), 

1986
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Figure A-19. Comparison of NCW and CTW Distributions and Geometric Mean (GM), 

1987–1989